#include<bits/stdc++.h>
using namespace std;
int main(){
	float t;
	cin>>t;
	if(20<=t&&t<=30) {
		cout<<"OK";
	}else cout<<"NO";
	
}
/**************************************************************
	Problem: 1302
	User: toughuatao1
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/