# include < stdio . h >

 int main ( void ) {
 int k , a , b ;

 scanf ("% d ", & k );
 scanf ("% d % d ", & a , & b );

 int largest = ( b / k ) * k ;
 if ( a <= largest ) {
 puts (" OK ");
 } else {
 puts (" NG ");
 }

 return 0;
}