#include <bits/stdc++.h>
using namespace std;
const int N = 105, M = 10005;
int n, m, a[N];
double x, f[N][M];
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> x;
  x /= 2;
  for (register int i = (1); i <= (n); ++i) cin >> a[i], m += a[i];
  f[0][0] = 1;
  for (register int i = (1); i <= (n); ++i)
    for (register int j = (i); j >= (1); --j)
      for (register int k = (m); k >= (a[i]); --k)
        f[j][k] += f[j - 1][k - a[i]] * j / (double)(n - j + 1);
  double ans = 0;
  for (register int i = (0); i <= (n - 1); ++i)
    for (register int j = (0); j <= (m); ++j)
      ans += f[i][j] *
             min((n / (double)(n - i) + 1) * x, (m - j) / (double)(n - i));
  cout << fixed << setprecision(10) << ans << '\n';
  return 0;
}
