public static string GetUrl(Stack<string> sta1,string bx)
{
int x;
if(bx=="b")
{x=sta.Top();}
else
{
Stack<sring> sta2=new Stack<string>();
x=int.parse(bx);
while(x>0)
  {
    sta2.Push(Sta.Pop());
    x=x-1;
  }
x=sta2.Top();
while(sta2.IsEmpty()==false)
 {
   sta.Push(sta2.Pop());
 }
}
return x;
}
}
}