#include <stdio.h>
int main(void){
  int K = 0;
  int A = 0;
  int B = 0;
  scanf("%d",&K);
  scanf("%d %d",&A,&B);
  int x = 0;
  int y = 0;
  x = A % K;
  y = A + (K - x);
  if (x == 0 || B < y){
    printf("OK");
  } else {
    printf("NG");
  }
  return 0;
}