#include <iostream>
using namespace std;

int main() {
    double weight, fee;
    cin >> weight;

    if (weight <= 10) {
        fee = 2.5;
    } else {
        fee = 2.5 + (weight - 10) * 1.5;
    }

    cout << fee << endl;
    return 0;
}
/**************************************************************
	Problem: 1043
	User: fandaohan
	Language: C++
	Result: Wrong Answer
****************************************************************/