#include<stdio.h>

int main (){
	int K,A,B;
	int sum=0;
	scanf("%d",&K);
	scanf("%d %d", &A,&B );
	while (sum<B){
		sum+=K;
		if (sum>A){
			break;
		}
	}
	sum>B?printf("NG\n"):printf("OK\n");
		
		
	
	return 0;
}