#include <iostream>
using namespace std;
int main()
{

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

in "else" you should use "b" instead of second "a".

Edited by author 20.12.2017 22:24