#include <bits/stdc++.h>
using ll = long long;
using namespace std;
const long long MOD = 1e9 + 7;
template <typename T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T>
bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
int main() {
  int R;
  cin >> R;
  cout << fixed << setprecision(6) << double(M_PI * R * R) << endl;
}
