#include <bits/stdc++.h>
using namespace std;
int dt[][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}, {0, 0}};
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  int r;
  cin >> r;
  double ans;
  double pi = acos(-1);
  ans = r * r * pi;
  cout << fixed << setprecision(5) << ans;
}
