#include <iostream>
#include <iomanip>

using ldouble = long double;

void solve() {
    ldouble n;
    std::cin >> n;

    std::cout << std::fixed << std::setprecision(1)
              << n * 3.5 << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}