#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    double r;
    cin>>n;
     
    if(n == 1){
        r = 5;
    }else if(n >= 2 && n <= 5){
        r = n * 4.5;
    }else if(n >= 6 && n <= 10){
        r = n * 4;
    }else if(n > 10){
        r = n * 3.5;
    }
     
    cout<<fixed<<setprecision(1)<<r;
}
/**************************************************************
	Problem: 1717
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:53 ms
	Memory:2072 kb
****************************************************************/