#include<stdio.h>
int main()
{
	int k, a, b, flag = 0, t;
	scanf("%d%d%d", &k, &a, &b);
	t = k;
	while (k <= b)
	{
		if (k >= a && k <= b) { flag = 1;break; }
		k = k + t;
	}
	if (flag == 0) { printf("NG"); }
	else { printf("OK"); }
	return 0;
}