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