#include <bits/stdc++.h>
using namespace std;
long double dp[103][10003];
int arr[103], N, X;
int main() {
  cin >> N >> X;
  dp[0][0] = 1;
  for (int i = 1; i <= N; ++i) {
    cin >> arr[i];
    for (int j = i; j; --j)
      for (int k = arr[i]; k <= 1e4; ++k)
        dp[j][k] += dp[j - 1][k - arr[i]] * j / (N - j + 1);
  }
  long double sum = 0;
  for (int i = 1; i <= N; ++i)
    for (int j = 1; j <= 1e4; ++j)
      sum += dp[i][j] * min((N + i) * X, j * 2) / i / 2;
  cout << fixed << setprecision(10) << sum;
  return 0;
}
