#include <iostream>
#include <iomanip>

int main() {
    int num;
    std::cin >> num;
    double price;
    if (num > 10) {
        price = num * 2 * 0.9;
    } else {
        price = num * 2;
    }
    std::cout << std::fixed << std::setprecision(1) << price << std::endl;
    return 0;
}    
/**************************************************************
	Problem: 1636
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/