#include<bits/stdc++.h>
using namespace std;
int main() {
	int n;
	cin>>n;
	if(n>=20&&n<=30)
		cout<<"OK";
	else
		cout<<"NO";
    return 0;
}

/**************************************************************
	Problem: 1302
	User: huangcanwu
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/