#include<stdio.h>
void main()
{
	int n;
	scanf("%d",&n);
	if(n>=20&&n<=30){
		printf("OK");
		
	}else{
		printf("NO");
		
	}
 } 
/**************************************************************
	Problem: 1302
	User: admin
	Language: C
	Result: Accepted
	Time:8 ms
	Memory:1144 kb
****************************************************************/