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