#include <bits/stdc++.h>
using namespace std;
int main(){
	int t;
 	cin>>t;
 	if(20<=t&&t<=30) cout<<"OK";
 	else cout<<"NO";


}
/**************************************************************
	Problem: 1302
	User: zhuangwenya
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/