#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <algorithm>
#include <functional>

using namespace std;


int main()
{
	long K, A, B;

	cin >> K >> A >> B;

	if (abs(A - B) >= K) 
		cout << "OK";
  	else if(B > 0 && K == 1)
      	cout << "OK";
	else
		cout << "NG";

	return 0;
}