#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1001001001;
const int MOD = 1000000007;
template <typename T>
void print(const T &v);
int main() {
  int R;
  cin >> R;
  cout << fixed << setprecision(10) << R * R * M_PI << endl;
  return 0;
}
template <typename T>
void print(T const &v) {
  for (int i = 0; i < v.size(); i++) {
    if (i) cout << " ";
    cout << v[i];
  }
  cout << endl;
}
