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

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