#include<bits/stdc++.h>
using namespace std;
int main(){
    int t;
	cin>>t;
	if(t>=20&&t<=30){
		cout<<"OK";
	}else{
		cout<<"NO";
	}	
}
/**************************************************************
	Problem: 1302
	User: xuezihong1
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/