#include<bits/stdc++.h>
using namespace std;
int main(){
	int t;
	cin>>t;
	if (20<=t && t<=30){
		cout<<"OK"<<endl;
	}
	else{
		cout<<"NO"<<endl;
	}
	return 0;
}
/**************************************************************
	Problem: 1302
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/