#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define fbo find_by_order
#define ook order_of_key

# define M_PI           3.14159265358979323846  /* pi */

typedef long long ll;
typedef pair<ll,ll> ii;
typedef vector<int> vi;
typedef long double ld;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    int r;
    cin>>r;
    cout<<r*r*M_PI*1.000000<<endl;
    return 0;
}
