#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
const int N = 1e5 + 5;
const int MOD = 1e9 + 7;
int main() {
  ll r;
  scanf("%lld", &r);
  printf("%.3lf\n", 1.0 * r * r * acos(-1.0));
  return 0;
}
