#include <iostream>
using namespace std;
int K, A, B;
int N;
int M;
int main() {
  cin >> K >> A >> B;
  N = A / K;
  M = B / K;
  if (M - N >= 1) {
    cout << "OK" << endl;
  } else {
    cout << "NG" << endl;
  }
  return 0;
}
