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

#define endl '\n'
#define ll long long
#define int long long
#define re register
#define pb(x) push_back(x)
#define ce(x) cout << x << '\n';

#define db  long double;
#define pll pair < ll, ll >;
#define scan(a, n) 		for(int i = 0; i < n; i++)cin >> a[i];

#define rep(i,x,n,inc) for(i=x ; i<n ; i+=inc)
#define repr(i,x,n,inc) for( i=x ; i>n ; i+=inc)
#define all(a)      (a).begin(),(a).end()
#define unique_sort(x) sort(all(x)), x.resize(distance(x.begin(), unique(all(x))))

#define mp(a,b) make_pair(a,b)
#define ff first
#define ss second
#define hell 1000000007
#define infl LLONG_MAX

#define Foxen(i,s) for (i=s.begin(); i!=s.end(); i++)
#define Fill(s,v) memset(s,v,sizeof(s))
#define cout_p(x, p) cout << fixed << setprecision((p)) << x << endl     //print with precision

#define tc(tt) \
    ll tt;    \
    cin >> tt; \
    for (ll _tt = 0; _tt < tt; _tt++) // testcase 

int32_t main() {
	ios::sync_with_stdio(0); 		cin.tie(0); cout.tie(0);

#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif

	ll t, i, x, j, y, 	z, k, n;
	cin >> n;
	cout_p((44 * n) / 7.0, 6);
}
