#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: admin
	Language: C++
	Result: Accepted
	Time:46 ms
	Memory:2072 kb
****************************************************************/