#include<iostream>
#include<string>

using std::cout;
using std::cin;
using std::endl;

int main(){
    int K,A,B,k;
    bool ans = true;
    cin >> K;
    k = K;
    cin >> A >> B;
    while(K <= B && ans){
        if(A <= K && K <= B){
            ans = false;
            cout << "OK";
        }
        K += k;
    }
    if(ans) cout << "NG";
}