#include <bits/stdc++.h>
using namespace std;
template <class T>
using vc = vector<T>;
template <class T>
using vvc = vc<vc<T>>;
template <class T>
void mkuni(vector<T>& v) {
  sort(v.begin(), v.end());
  v.erase(unique(v.begin(), v.end()), v.end());
}
template <class T>
void print(T x, int suc = 1) {
  cout << x;
  if (suc == 1)
    cout << '\n';
  else
    cout << ' ';
}
template <class T>
void print(const vector<T>& v, int suc = 1) {
  for (int i = 0; i < v.size(); i++)
    print(v[i], i == (int)(v.size()) - 1 ? suc : 2);
}
const int INF = 0x3f3f3f3f;
const int maxn = 105;
double C[maxn][maxn];
void db() {
  for (int i = 0; i < maxn; i++) {
    C[i][0] = 1;
    for (int j = 1; j <= i; j++) C[i][j] = C[i - 1][j] + C[i - 1][j - 1];
  }
}
const int maxv = 1e4 + 7;
double dp[maxn][maxv];
int main() {
  db();
  int n, x;
  scanf("%d%d", &n, &x);
  int tot = 0;
  dp[0][0] = 1;
  for (int i = 1, tmp; i <= n; i++) {
    scanf("%d", &tmp);
    tot += tmp;
    for (int k = i - 1; k >= 0; k--)
      for (int j = tmp; j < maxv; j++) dp[k + 1][j] += dp[k][j - tmp];
  }
  double ans = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < tot; j++) {
      if (!dp[i][j]) continue;
      ans += dp[i][j] / C[n][i] *
             min(1.0 * (tot - j) / (n - i), (1.0 + 0.5 * i / (n - i)) * x);
    }
  printf("%.12f\n", ans);
}
