#include <bits/stdc++.h>
/*
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
namespace mp = boost::multiprecision;
using bint = mp::cpp_int;
*/
#include <atcoder/all>
#include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <random>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define repp(i,n,m) for (int i = m; i < (n); ++i)
using namespace std;
using namespace atcoder;
using namespace internal;
//alias g++='g++ -I/mnt/c/Users/Owner/Desktop/ac-library'
using ll = long long;
using ld = long double;
using P = pair<int, int>;
using PI = pair<pair<int,int>,int>;
using PL = pair<long long, long long>;
using PLL = pair<pair<long long, long long>, long long>;
using Pxy = pair<long double, long double>;
const int INF = 1001001007;
const int modd = 1000000007;
const long long modl = 1000000007LL;
const long long mod = 998244353LL;
const ll inf = 2e18;

template <typename SA>
void priv(vector<SA> &ar){
    rep(i,ar.size()-1) cout << ar[i] << " ";
    cout << ar[ar.size()-1] << endl;
}
template <typename SB>
void privv(vector<vector<SB>> &ar){
    rep(i,ar.size()){
        rep(j,ar[i].size()-1) cout << ar[i][j] << " ";
        cout << ar[i][ar[i].size()-1] << endl;
    }
}
template <typename SC>
bool range(SC a, SC b, SC x){return (a <= x && x < b);}
bool rrange(P a, P b, P xy){
    bool s = range(a.first,b.first,xy.first);
    bool t = range(a.second,b.second,xy.second);
    return (s && t);
}
template <typename SD>
void sor(vector<SD> &ar){sort(ar.begin(),ar.end());}
template <typename SE>
void rev(vector<SE> &ar){reverse(ar.begin(),ar.end());}
template <typename SF>
bool chmin(SF &a, const SF &b){if(a>b){a = b; return true;} return false;}
template <typename SG>
bool chmax(SG &a, const SG &b){if(a<b){a = b; return true;} return false;}
template <typename SH>
void eru(vector<SH> &ar){sor(ar);ar.erase(unique(ar.begin(),ar.end()),ar.end());}
template <typename SI>
SI   last(vector<SI> &ar){return ar[ar.size()-1];}
template <typename SJ>
SJ   cel(SJ a, SJ b){if (a % b == 0) return a/b; return a/b +1;}
template <typename SK, typename SL>
void pout(pair<SK,SL> p) {cout << p.first << " " << p.second << endl;}

void yes(){cout << "Yes" << endl;}
void no (){cout << "No" << endl;}
void yn (bool t){if(t)yes();else no();}
void Yes(){cout << "YES" << endl;}
void No (){cout << "NO" << endl;}
void YN (bool t){if(t)Yes();else No();}
void dout() {cout << setprecision(20);}

vector<int> dx = {0,1,0,-1};
vector<int> dy = {1,0,-1,0};
const string ALP = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string alp = "abcdefghijklmnopqrstuvwxyz";

ll gcds(ll a, ll b){
    ll c = a % b;
    while (c != 0){
        a = b;
        b = c;
        c = a % b;
    }
    return b;
}

int main(){
    ld x; cin >> x;
    x *= 4.0;
    dout(); cout << x << endl;
}