{$APPTYPE CONSOLE}
{$n+}
uses
  SysUtils;

type
  tpoint=record
           x,y:{longint} extended;
         end;
const
  maxn=200;
var
  a:array[1..maxn] of tpoint;
  n:longint;
  min:extended;
  f:tpoint;
procedure init;
var
  i:longint;
begin
  assign(input,'input.txt');
  reset(input);
  assign(output,'output.txt');
  rewrite(output);
  readln(f.x,f.y,n);
  for i:=1 to n do
    readln(a[i].x,a[i].y);
  inc(n);
  a[n+1].x:=a[1].x;
  a[n+1].y:=a[1].y;
  min:=maxlongint;
end;
function scalmul(p1,p2,p3,p4:tpoint):extended;
begin
  scalmul:=(p2.x-p1.x)*(p4.x-p3.x)+(p2.y-p1.y)*(p4.y-p3.y);
end;
function rast(p1,p2:tpoint):extended;
begin
  rast:=sqrt(sqr(p2.x-p1.x)+sqr(p2.y-p1.y));
end;
function vecmul(p1,p2,p3,p4:tpoint):extended;
begin
  vecmul:=(p2.x-p1.x)*(p4.y-p3.y)-(p2.y-p1.y)*(p4.x-p3.x);
end;
function prov:boolean;
var
  i,j:longint;
  b:boolean;
begin
  b:=true;
  for i:=1 to n-1 do
    if vecmul(a[i],f,a[i],a[i+1])>=0 then begin
      if b then b:=false;
    end;
  prov:=b;
end;
procedure solve;
var
  i,j,im,l,r:longint;
  h:extended;
begin
  if prov then begin
    writeln(0.0:0:3);
    halt;
  end;
  dec(n);
  for i:=1 to n do
    if rast(f,a[i])<min then begin
       min:=rast(f,a[i]);
       im:=i;
    end;
  l:=i-1;
  r:=i+1;
  if l<1 then inc(l,n);
  if r>n then dec(r,n);
  if (scalmul(a[l],f,a[l],a[im])>0) and (scalmul(a[im],f,a[im],a[l])>0) then begin
    h:=vecmul(f,a[im],f,a[l])/rast(a[im],a[l]);
    if min>h then min:=h;
  end;
  if (scalmul(a[r],f,a[r],a[im])>0) and (scalmul(a[im],f,a[im],a[r])>0) then begin
    h:=vecmul(f,a[im],f,a[r])/rast(a[im],a[r]);
    if min>h then min:=h;
  end;
end;
procedure done;
begin
  writeln(abs(min*2):0:3);
end;
begin
  init;
  solve;
  done;
end.

in 4 test answer 0.000 (100%)(так что думай)

yeah
I have writtln 0 and I got WA at #4test
then i wrote 0.000 and got AC

I didn't understand where was the mistake in the code... if you have true code can you send me it on my e-mail, please?
my e-mail : liwang@mail.ru
I can send you any code if I have solved it. don't look to my account. just send me the number that you want. if I have it I will send you in return for this problem. thank you