#include<bits/stdc++.h>
using namespace std;

int main() {
    int n;
    cin >> n; // 输入整数n
    if(n>=20&&n<=30){
        cout<<"OK"<<endl;
    }else{
    	cout<<"NO"<<endl;
	}
}
/**************************************************************
	Problem: 1302
	User: zhengzihao
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/