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

int main() {
  int A, B, K;
  cin >> K;
  cin >> A;
  cin >> B;
  
  int r = A % K;
  if ((r == 0) || ((r + B - A) >= K)) {
    cout << "OK";
  } else {
    cout << "NG";
  }
  
  return 0;
}