var value:array[0..100000] of longint;
    prev:array[0..100000] of word;
    top:array[0..1000] of word;
    n,i,j,k,c:longint; s:string;
begin
  {assign(input,'input.txt');
  reset(input);}
  readln(n);
  fillchar(prev,sizeof(prev),0);
  fillchar(top,sizeof(top),0);
  for i:=1 to n do begin
      readln(s);
      if pos('PUSH',s)<>0 then begin
         delete(s,1,5);
         val(copy(s,1,pos(' ',s)-1),j,c);
         delete(s,1,pos(' ',s));
         val(s,k,c);
         value[i]:=k; prev[i]:=top[j];
         top[j]:=i;
         end
         else begin
         delete(s,1,4);
         val(s,j,c);
         writeln(value[top[j]]);
         top[j]:=prev[top[j]];
         end;
      end;
end.

Thank you, I got AC now!

var i,j,n,l,k,t,zhen:longint;
    ch:char;
    a:array[0..100001]of longint;
    b:array[0..100000]of word;
begin
     readln(n);
     fillchar(a,sizeof(a),0);
     fillchar(b,sizeof(b),0);
     zhen:=1;
     for i:=1 to n do
     begin
          for j:=1 to 2 do read(ch);
          if ch='o' then begin
             read(ch);read(ch);
             readln(t);
             for j:=zhen-1 downto 1 do
                 if b[j]=t then begin
                    writeln(a[j]);
                    b[j]:=-1000;
                    break;
                    end;
                    end
                    else
                        begin
                             read(ch);read(ch);read(ch);read(t);
                             b[zhen]:=t;
                             readln(t);
                             a[zhen]:=t;
                             inc(zhen);
                             end;
     end;
end.