#include <stdio.h>
int main(void){
    int n;
    int a, b;
    scanf("%d", &n);
    scanf("%d %d", &a, &b);
    if( n == 1) printf("OK\n");
    else if( (b - a) <= (n - 1) ) printf("NG\n");
    else printf("OK\n");
    return 0;
}
