#include<stdio.h>
int main(){
  int unused __attribute__((unused));
  int K, A, B, i, tmpK = 0, t = 0;
  unused = scanf("%d", &K);
  unused = scanf("%d %d", &A, &B);

  i=1;
  while(tmpK <= 1000){
    tmpK = i*K;
    if(A <= tmpK && tmpK <= B) t = 1;
    i++;
  }
  if(t==1) printf("OK");
  else printf("NG");
  return 0;
}