#include<bits/stdc++.h>
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: admin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/