Стек
var s:string; c:char; i:integer; f:boolean;
begin
readln(s);
top:=0;
f:=true;
for i:=1 to length(s) do
  begin
   if s[i]='(' then push(s[i])
     else
      begin
       c:=pop;
       if c<>'(' then
        f:=false;
      end;
  end;
if f=true then
  writeln('OK')
 else
  writeln('Ne ok');
end.