#include <stdio.h>

int main(void) {
	Int k, a, b;
	
	scanf("%d", &k);
	scanf("%d%d", &a, &b);
	
	int largest = (b / k) * k;
	if (a <= largest) {
		puts("OK");
	} else {
		puts("NG");
	}
	return 0;
}
