#include <bits/stdc++.h>
using namespace std;
long long gcdExtended(long long a, long long b, long long *x, long long *y) {
  if (a == 0) {
    *x = 0;
    *y = 1;
    return b;
  }
  long long x1, y1;
  long long gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
void diophantine(long long a, long long b, long long c, long long *c1,
                 long long *c2) {
  long long x, y;
  long long d = gcdExtended(a, b, &x, &y);
  c = c / d;
  *c1 = x * c;
  *c2 = y * c;
}
int main(void) {
  long long n;
  cin >> n;
  vector<long long> v(n);
  for (int i = 0; i < n; i++) cin >> v[i];
  sort(v.begin(), v.end());
  long long ans = 0;
  for (int i = n - 1; i >= 0; i--) {
    ans += v[i] * v[i];
    i--;
    if (i >= 0) ans -= v[i] * v[i];
  }
  cout << ans * acos(-1) << endl;
}
