#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < n; i++) {
    cin >> v[i];
  }
  sort(v.begin(), v.end());
  int i = n - 1;
  int count = 0;
  double sum = 0;
  while (i >= 0) {
    count++;
    if (count % 2) {
      sum = sum + 3.1415926536 * (v[i]) * (v[i]);
    } else {
      sum = sum - 3.1415926536 * (v[i]) * (v[i]);
    }
    i--;
  }
  cout << sum << endl;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t;
  t = 1;
  while (t--) {
    solve();
  }
}
