#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    if(n<=30&&n>=20) cout<<"OK";
    else cout<<"NO"; 
    return 0;   
}
/**************************************************************
	Problem: 1302
	User: lijinkai
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/