#include <bits/stdc++.h>
using namespace std;
double cc[111][111], f[11111][111], pf[11111][111];
int c[1111];
int main() {
  {
    if (fopen("input.txt", "r")) {
      freopen("input.txt", "r", stdin);
      freopen("output.txt", "w", stdout);
    }
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
  }
  cc[0][0] = 1;
  for (int n = 1; n <= 100; ++n) {
    cc[n][0] = 1;
    for (int k = 1; k <= 100; ++k) cc[n][k] = cc[n - 1][k - 1] + cc[n - 1][k];
  }
  int n, x;
  cin >> n >> x;
  double S = 0;
  for (int i = 0; i != n; ++i) {
    cin >> c[i];
    S += c[i];
  }
  f[0][0] = pf[0][0] = 1;
  for (int i = 0; i != n; ++i) {
    for (int k = 1; k <= 100; ++k)
      for (int s = 0; s <= 10000; ++s)
        if (s - c[i] >= 0) f[s][k] += pf[s - c[i]][k - 1];
    for (int k = 0; k <= 100; ++k)
      for (int s = 0; s <= 10000; ++s) pf[s][k] = f[s][k];
  }
  double ans = 0;
  for (int k = 0; k < n; ++k)
    for (int s = 0; s <= 10000; ++s)
      ans += f[s][k] * 1.0 / cc[n][k] *
             min((S - s) * 1.0 / (n - k), x / 2.0 * (1.0 + n * 1.0 / (n - k)));
  cout << fixed;
  cout.precision(12);
  cout << ans;
  return 0;
}
