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

#define ll long long int
#define fastio ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);

const int mod = 1e9 + 7;
const int N = 200001;


void solve() {
    int n;
    cin >> n;
    double ans = 2 * 22 * n;
    ans = ans / 7;
    cout << fixed << setprecision(10) << ans ;
}

/*
 */

int main()
{
    fastio
    int testcase = 1;
    //cin >> testcase ;
    
    while(testcase --) {
        solve();
        cout << '\n';
    }
    
    return 0;
}
 

