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