#include <bits/stdc++.h>
using std::cin;
using std::cout;
using std::endl;
using std::pair;
using std::string;
using std::vector;
void debug_out() { cout << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}
template <class T>
bool updatemMax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool updateMin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
int main() {
  double R;
  cin >> R;
  double pi = 3.14159;
  cout << (pi * R * R) << endl;
}
