#include <bits/stdc++.h>
using namespace std;
int n, x, s;
int a[105];
double f[105][10005];
int main() {
  cin >> n >> x;
  for (int i = 1; i <= n; i++) cin >> a[i], s += a[i];
  f[0][0] = 1;
  for (int i = 1; i <= n; i++)
    for (int j = i; j >= 1; j--)
      for (int k = s; k >= a[i]; k--)
        f[j][k] += f[j - 1][k - a[i]] * j / (n - j + 1);
  double ans = 0;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= s; j++)
      ans += f[i][j] * (min((n + i) * x, j * 2) / 2.0) / i;
  printf("%.10lf", ans);
  return 0;
}
