#include <bits/stdc++.h>
using namespace std;
template <typename T>
void solve() {
  int n, x;
  cin >> n >> x;
  vector<int> cs(n);
  for (auto& c : cs) {
    cin >> c;
  }
  int c_sum = accumulate(cs.begin(), cs.end(), 0);
  vector<vector<T>> mass(n + 1, vector<T>(c_sum + 1, 0));
  mass[0][0] = T(1);
  for (int c : cs) {
    for (int k = n - 1; k >= 0; --k) {
      for (int s = c_sum - c; s >= 0; --s) {
        mass[k + 1][s + c] += T(k + 1) / T(n - k) * mass[k][s];
      }
    }
  }
  T answer(0);
  for (int k = 1; k <= n; ++k) {
    for (int s = 0; s <= c_sum; ++s) {
      answer +=
          min(T(s) / T(k), T(x) / T(2) * (T(1) + T(n) / T(k))) * mass[k][s];
    }
  }
  printf("%.17f\n", (double)answer);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  solve<double>();
  return 0;
}
