#include <bits/stdc++.h>
using db = double;
db f[107][10007];
int a[107];
int main() {
  int n, x, sum = 0;
  db ans = 0;
  scanf("%d%d", &n, &x), f[0][0] = 1;
  for (int i = 1; i <= n; ++i) scanf("%d", a + i), sum += a[i];
  for (int i = 1; i <= n; ++i)
    for (int j = n; j; --j)
      for (int k = a[i]; k <= sum; ++k)
        f[j][k] += f[j - 1][k - a[i]] * j / (n - j + 1);
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= sum; ++j)
      ans += f[i][j] * std::min((n + i) * x, j * 2) / i;
  printf("%.10lf", ans / 2);
}
