#include <iostream>
#include <iomanip> 
using namespace std;

int main() {
    int bottle_num;  
    cin >> bottle_num;

    double unit_price;  
    if (bottle_num == 1) {
        unit_price = 5.0;
    } else if (bottle_num >= 2 && bottle_num <= 5) {
        unit_price = 4.5;
    } else if (bottle_num >= 6 && bottle_num <= 10) {
        unit_price = 4.0;
    } else if (bottle_num > 10) {
        unit_price = 3.5;
    }

    double total = bottle_num * unit_price; 
    cout << fixed << setprecision(1) << total << endl;

    return 0;
}
/**************************************************************
	Problem: 1717
	User: fuhoubin
	Language: C++
	Result: Accepted
	Time:66 ms
	Memory:2072 kb
****************************************************************/