#include<bits/stdc++.h>
#define lli long long int
#define MOD 1000000007
#define KING 1000000002
#define queen 1000002
#define fi first
#define se second
#define se second
#define lsb(i) (i & -i)
#define nl cout<<'\n'
#define TEST cout<<"TEST",nl
#define pr pair<lli,lli>
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define vi vector<lli>
#define vpi vector<pr> 
#define P pair<lli,pr>
#define fastIO ios_base::sync_with_stdio(false); cin.tie(NULL)
#define NA(i,s,n) for(lli i=s;i<n;i++)
using namespace std;

void solve(){
    lli n; cin>>n; 
    float d = (2*22*n)/7.0;
    cout<<d<<'\n';
    return;
}
int main(){
    fastIO;
    lli t = 1,p; 
    // cin>>t; p = t;
    NA(i,0,t) {
        solve();
    }
    return 0;
}