#include <bits/stdc++.h>
using namespace std;

int main() {
  string S, T = "OK";
  while (cin >> S) {
    if (S.size() != 1 && S.at(0) == '0') T = "NG";
    for (int i = 0; i < S.size(); i++) if (!isdigit(S.at(i))) T = "NG";
  }
  cout << T << "\n";
}