#include <stdio.h>

int main() 
{

    int a, b;
    int k;
    int num = 0;

    scanf("%d %d %d", &k, &a, &b);
    while ( (num*k) < b){
        num++;
        if((num*k)>= a && (num*k) <= b){
            printf("OK");
            return 0;
        }

    }
    printf("NG");
    return 0;

}
