#include<stdio.h>

int main() {
  int k, a, b,num=0;
  scanf("%d", &k);
  scanf("%d %d", &a, &b);
  num = a / k;
  num *= k;
  num += k;
  if(num < b || b % k == 0 || a % k == 0) printf("OK");
  else printf("NG");
}