#include <bits/stdc++.h>
 
#define ll long long
#define vi vector<int>
#define vll vector<long long>
#define si set<int>
#define stk stack<int>
#define que queue<int>
#define pb push_back
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<ll,ll>
#define IOS ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
const ll mod=1e9+7;
 
using namespace std;

int main(){
	int q=1;
	//cin>>q;
	while(q--){
		int n;
		cin>>n;

		cout<<setprecision(4)<<(44/(float)7)*n<<endl;
	}
   
}