#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef string str;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    ll a;
    cin >> a;
    double kq = a * 3.5;
    cout << fixed << setprecision(1) << kq << "\n";
    return 0;
}