I have AC this code in another site:
http://www.olymp.vinnica.ua/alltask/task.shtml?coins
But here a have WA1. Wats wrong in my code?

program Stone_pile;
const size=20;
var a:array[1..20]of longint;
    c:array[0..size] of shortint;
    i,g1,g2,raz,j,z,kol,n:longint;

procedure ReadFile;
begin
   { assign(input,'in.txt');
     reset(input);}
     read(n);
     for i:=1 to n-1 do readln(a[size-i+1]);
     readln(a[1]);
     fillchar(c,sizeof(c),0);
     kol:=1;
     for i:=1 to n-1 do kol:=kol*2;
     dec(kol);
     raz:=MaxLongint;
end;

begin
     ReadFile;
     for z:=1 to kol+1 do
     begin
          g1:=a[1];
          g2:=0;
          for j:=size downto size-n+2 do
              if c[j]=0 then inc(g1,a[j])
              else inc(g2,a[j]);
          if abs(g1-g2)<raz then raz:=abs(g1-g2);

          inc(c[size]);
          for j:=size downto size-n+2 do if c[j]>1 then
          begin
               inc(c[j-1],c[j] div 2);
               c[j]:=c[j] mod 2;
          end;
      end;

     writeln(raz);
end.