#include<bits/stdc++.h>
using namespace std;
int main() {
    int n;
    cin>>n;
    if(n<10){
    	cout<<n*1.5;
    }if(n<=10){
    	cout<<9*1.5+(n-9)*1.2;
    }
    return 0;
}
/**************************************************************
	Problem: 1630
	User: panjinyan
	Language: C++
	Result: Wrong Answer
****************************************************************/