//
// Matching parentheses: tell if parens don't match, and give position in
// file if the problem is an extra right paren.  "count" keeps track of how
// deeply nested we currently are.
//

#include<iostream.h>
const char LEFT = '(';
const char RIGHT = ')';

int main(void)
{
  int count = 0, position=0;
  char letter;
  cin.unsetf(ios::skipws);   // let's not skip whitespace
  while (cin >> letter) {    // expression evaluates to 0 on EOF
    position = position + 1;
    if (letter == LEFT) ++count;
    if (letter == RIGHT) --count;
    if (count < 0) {
      cout << "extra right parenthesis at position " << position << endl;
      return 0;
    }
  }
  if (count > 0) cout << "too many left parentheses" << endl;
  else cout << "OK." << endl;
  return 0;
}