/*
Jackson Simoneau
SI@UCF 2026 - Intro to Competitive Programming

Solution to https://open.kattis.com/problems/areal
*/

#include <bits/stdc++.h>
using namespace std;

int main() {
    //Read in the area of the square as a double
    double a;
    cin >> a;

    //Make sure to set the precision to at least 6 decimal places!
    cout << setprecision(10) << fixed;
    cout << sqrt(a)*4 << endl;
}