#include <bits/stdc++.h>
using namespace std;
double f[105][10005];
int c[105];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0), cout.tie(0);
  int n, x, sum = 0;
  cin >> n >> x;
  for (int i = 1; i <= n; ++i) cin >> c[i], sum += c[i];
  f[0][0] = 1;
  for (int i = 1; i <= n; ++i)
    for (int j = i; j; --j)
      for (int k = c[i]; k <= sum; ++k)
        f[j][k] += f[j - 1][k - c[i]] * j / (n - j + 1);
  double ans = 0;
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= sum; ++j)
      ans += f[i][j] * min((n + i) * x / 2.0, 1.0 * j) / i;
  cout << setprecision(9) << fixed << ans << '\n';
  return 0;
}
