#include <bits/stdc++.h>
using namespace std;
int fuctrial(int n) {
  if (n == 1) return 1;
  return n * fuctrial(n - 1);
}
int dSum(int x[], int N, int s) {
  int ret = 0;
  if (N == 1) {
    return s;
  }
  int y[N - 1];
  for (int(k) = 0; (k) < (N - 1); (k)++) {
    for (int(i) = 0; (i) < (N - 1); (i)++) {
      if (i < k) {
        y[i] = x[i];
      } else {
        y[i] = x[i + 1];
      }
    }
    ret += dSum(y, N - 1, s + x[k + 1] - x[k]);
  }
  return ret;
}
int main() {
  int N;
  cin >> N;
  int x[N];
  for (int(i) = 0; (i) < (N); (i)++) cin >> x[i];
  int n = dSum(x, N, 0);
  double result = n * 1.0 / N;
  result *= fuctrial(N - 1);
  cout << n << endl;
  return 0;
}
