#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
mt19937 gen(chrono::high_resolution_clock::now().time_since_epoch().count());
template <typename... Args>
void write(Args... args) {
  ((cout << args << " "), ...);
  cout << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  const double pi = 3.1415927;
  int x;
  cin >> x;
  cout << pi * x * x;
  return 0;
}
