#include<stdio.h>
int main()
{
int j,K,A,B,count=0;
scanf("%d %d %d",&K,&A,&B);
for(j=1;j<=1000;j++)
{
if(K*j>=A && K*j<=B)
 {
 printf("OK\n");
 count=count+1;
 break;
 }
}
if(count==0)
printf("NG\n");
return 0;
}