#include<iostream>
using namespace std;
int main()
{
   int t;
   cin>>t;
   if(t>=20&&t<=30){
   	   cout<<"OK";
   }
   else{
   	   cout<<"NO";
   }	     
    return 0;
}
/**************************************************************
	Problem: 1302
	User: chenmingyu
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/