#include <bits/stdc++.h>
using std::cerr;
using std::endl;
const int N = 101, M = 10001;
int n, x, v[N], sum;
double f[N][M], ans;
int main() {
  std::cin >> n >> x;
  for (int i = 1; i <= n; ++i) std::cin >> v[i], sum += v[i];
  f[0][0] = 1;
  for (int i = 1; i <= n; ++i)
    for (int j = i; j; --j)
      for (int k = v[i]; k <= sum; ++k)
        f[j][k] += f[j - 1][k - v[i]] * j / (n - j + 1);
  for (int i = 0; i < n; ++i)
    for (int j = 0; j <= sum; ++j)
      ans += f[i][j] * std::min((1.0 * n / (n - i) + 1) * x / 2,
                                1.0 * (sum - j) / (n - i));
  printf("%.12lf\n", ans);
  return 0;
}
