#include<bits/stdc++.h>
using namespace std;
int main(){
    int t;
    cin>>t;
    if(t>=20&&t<=30){
        cout<<"OK";
    }else{
        cout<<"NO";
    }   
}
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
/**************************************************************
	Problem: 1302
	User: zhangyilei
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/