#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define vi vector<int>
#define vvi vector<vector<int> >
#define vb vector<bool>
#define vpii vector<pair<int,int> >
#define pii pair<int,int>
#define mii map<int,int>
#define mod 1000000007
#define pb push_back
#define ff first
#define ss second
#define mkp make_pair
#define input(a,b,n) for(i=b;i<n;i++){cin>>a[i];}
#define print(a,b,n) for(i=b;i<n;i++){cout<<a[i]<<" ";}cout<<endl;
const int inf=0x3f3f3f3f3f3f3f3f;
int power(int a, int b){
    int res = 1;
    while(b!=0){
        if(b&1){
            res *= a; 
        }
        a = (a * a);
        b = (b / 2);
    }
    return res;
}
int32_t main()
{
	ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int r;
  cin>>r;
  double x=22/7*r*r;
  cout<<x<<endl;
    return 0;
}
