#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    if(n>=20){
        if(n<=30){
            cout<<"OK";
        }
    }else{
        cout<<"NO";
    }
}
/**************************************************************
	Problem: 1302
	User: yangjunwen
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/