i kinda changed the variables
a = the first sum suggested by petr
b = the ---------------------- taxi driver
c = amount added by petr everytime
d = ---------------- taxi driver
we can say that at step n of bargaining:
petr -> a + n*c
taxi -> b - n*d

where looking for a time when petr's suggestion is less than the drivers
which means a + nc <= c - n*d
but there sometime when petr suggest more than what the driver suggest the previous time.
that's why i am comparing between the last petr's suggestion and the previous one of the driver a+c*n > b-d*(n-1). in this case petr says ok to the taxi driver and do not suggest more than that.


void solve() {
    int a, c, b, d;
    cin >> a >> c >> b >> d;
    if (a >= b) {
        cout << a;
        return;
    }
    int n = (b-a)/(c+d);
    if ((b-1)%(c+d)!=0) n++;
    if (a+c*n > b-d*(n-1)) {
        cout << b - d*(n-1) << ln;
    }
    else {
        cout << a + n*c << ln;
    }
}


Edited by author 10.09.2022 21:11

Очень хитрая задача, так как в условии не сказано или а меньше с или с меньше а поэтому нужно рассматривать 2 варианта.
Вот правильный код:
#include<iostream>
using namespace std;
int main()
{
    int a,b,c,d,e;
    cin >> a >> b >> c >> d;
    if( a <= c)
    {
        while(a <= c)
    {
        if( a + b <= c)
        {
           a = a + b;
           e = a;
        }
        else {e = c;break;}

        if( c -d >= a)
        {
            c = c - d;
            e = c;
        }
        else {e = a;break;}
    }
    cout << e << endl;
    }
    else
        cout << a << endl;
    return 0;
}

#include <bits/stdc++.h>

using namespace std;

#define go ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
typedef long long ll;

int main() {
    go
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    while(a < c){
        if(a+b > c) break;
        a += b;
        c -= d;
    }
    cout << max(a, c);

    return 0;
}

The key to solve is that : Driver won't take less than offered, and Petr won't pay more than asked. So if you using a loop for example in each step a will be always min(a + b, c) and c will always be max(c - d, a)

#include <iostream>
using namespace std;

int main()
{
    long long a, b, c, d;
    int r = 0, g;
    cin >> a >> b;
    cin >> c >> d;
    g = (a + b * (c - a + d) / (b + d)) - ((a + b * (c - a + d) / (b + d)) % b);
    cout << g << endl;
    return 0;
}

            Thread.CurrentThread.CurrentCulture = CultureInfo.InvariantCulture;

            var tokens = Console.ReadLine().Trim().
                Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries);

            var a = int.Parse(tokens[0]);
            var b = int.Parse(tokens[1]);
            var c = int.Parse(tokens[2]);
            var d = int.Parse(tokens[3]);

            var min = a + (c - a) / (b + d) * b;
            var max = c - (c - a) / (b + d) * d;

            min = Math.Min(min + b, Math.Max(min, max));
            max = Math.Max(max - d, min);

            Console.WriteLine(max);

#include<iostream>
using namespace std;

int main(){
    int petr,a,taxi,b;
    int temp;

    while(cin>>petr>>a>>taxi>>b){
        if(petr>=taxi)cout<<petr<<endl;

        else{
            temp=taxi-petr;
            if(a<=b){
                while(temp>b){
                    petr+=a,taxi-=b;
                    temp=taxi-petr;
                }
                cout<<petr+a<<endl;
            }
            else{
                while(temp>a){
                    petr+=a,taxi-=b;
                    temp=taxi-petr;
                }
                cout<<taxi<<endl;
            }
        }
    }
}

i pass all the test that the discuss give
but i still get wa at #4
could u give me some new test?

Please help me.I always have WA#4.
Give me any tests.
THAnk!!!><

Что нужно поправить,чтобы эта программа реализовывала тест '60 100 300 1'?вообще она ломается на 10 тесте при сдаче, но после того как я посмотрела обсуждения и прогнала её по найденным тестам  поняла что не могу реализовать только один выше сказанный ответ кстати (как я думаю) 298.
вот тесты на которых пробовала.
к стати я очень невнимательная, поэтому сильно на меня не ругаться )))
150 50 1000 100
ответ - 450

1 4 2 2
ответ - 2

1 3 5 2
ответ - 4

2 1 1 1
ответ - 2

1 3 4 3
ответ - 4

1000 2 2000 3
ответ - 140

11 1 10 2
ответ - 11

4 3 6 1
ответ - 6

1 2 12 3
ответ - 6

var a,b,c,d:integer;
begin
read(a,b,c,d);
if a>c then write(a)
else
begin
while a<>c do
begin
a:=a+b;
if (a>c-d)and(c>a) then c:=a
         else if a+b>c then a:=c
                     else if a=c then break
                                 else c:=c-d;
end;
write(c);
end;
end.

Заранее спасибо)♥_♥

Edited by author 28.12.2017 21:55

Edited by author 28.12.2017 21:56

var a,b,c,d,cen,k:integer;
begin
read(a,b,c,d);
while k<>1 do begin
if (a+b>c) then begin
k:=1;cen:=c;end
else a:=a+b;
if(c-d<a)then begin
k:=1;cen:=a;end
else c:=c-d;end;
writeln(cen);
end.

#include <iostream>

using namespace std;

int main()
{
    int a,b,c,d;
    cin>>a>>b>>c>>d;
        for (int i=0;a<c;i++)
        {
            a+=b;
            c=c-d;
        }
        cout<<a;
}


what's the problem??? help me please

var
a,b,c,d:integer;
begin
Read(a,b,c,d);
While a<>c do
      begin
      a:=a+b;
      c:=c-d
      end;
a:=c;
WriteLn(a);
end.


Почемууу((
Why(((

#include<iostream>
#include<math.h>
#include<algorithm>
#include<string.h>

using namespace std;
int a,b,c,d;
int main()
{
    cin >> a >> b >> c >> d;
    int h = c;
    if(a >= c)
    {
        cout << a;
        return 0;
    }
    while(1)
    {
        if(a == c)
        {
            cout << a;
            return 0;
        }
        a+=b;
        if(c-d >= a) c-=d; else
        {
            if(a > h) cout << h; else
            cout << a;
            return 0;
        }
    }
    return 0;
}

#include<stdio.h>
#include<math.h>
int main()
{
    int a,b,c,d,i,t;
    scanf("%d %d %d %d",&a,&b,&c,&d);

    for(i=1;i<10000;i++)
    {
        a=a+b;
        if(a>c)
        {
            t=c;
            break;
        }
        c=c-d;
        if(a>=c)
        {
            t=a;
            break;
        }
    }
    printf("%d",t);
    return 0;
}

for 150 400 1000 200:
150 1000
550 800*
950 600
how is the answer 800 and not 950 ??

for 100 100 150 20:
100 150*
200 130
why is the answer 150 and not 200 ??

for 1 2 12 3:
1 12
3 9
5 6*
7 5
why is the answer 6 and not 7 ??

for 3 3 5 2:
3 5*
6 3
why is the answer 5 and not 6 ??
Please help!

Edited by author 16.03.2015 23:24

Could someone tell me what WA - 3 is. all the test cases are working with the expected output but still get WA 3. NOt sure where the problem is. Kindly help.

Test 1:
150 50 1000 100
200 900
250 800
300 700
350 600
400 500
450 400
Answer:450
Test 2:
1 2 12 3
3 9
5 6
7 3
Answer:6
Test 3:
4 3 6 1
Answer:6
Test 4:
11 1 10 2
Answer:11
Test 5:
1000 2 2000 3
.............
.............
1388 1418
1390 1415
1392 1412
1394 1409
1396 1406
1398 1403
1400 1400
Answer:1400

here's my text:

program Project2;
var a,b,c,d:longint;
begin
 readln (a,b,c,d);

 while c>a do begin
a:=a+b;
c:=c-d;
  end;
if c=a+b then
   writeln (c)
else writeln (a);

end.


what's the problem??? help me please

#include <iostream>
using namespace std;
int main(){
    int a,b,c,d,k=0;
    cin >> a >> b >> c >> d;
    while(a<c){
        if(k==0){
            k = 1;
            a += b;
            cout << a << " ";
        } else {
            k = 0;
            c -= d;
            cout << c << " ";
        }
    }
    cout << a ;
    return 0;
}

hi everybody! i have wa 5 but i don't understand my mistake. can anybody who knows some tests help me?