#include <bits/stdc++.h>
using namespace std;
const int N = 128;
const int M = 1e4 + 5;
int n, x, s, a[N];
double dp[N][M], C[N], ans;
int main() {
  scanf("%d%d", &n, &x);
  for (int i = 1; i <= n; ++i) scanf("%d", a + i), s += a[i];
  C[0] = 1;
  for (int i = 1; i <= n; ++i) C[i] = C[i - 1] / i * (n - i + 1);
  dp[0][0] = 1;
  for (int i = 1; i <= n; ++i)
    for (int j = n; j >= 1; --j)
      for (int k = a[i]; k <= s; ++k) dp[j][k] += dp[j - 1][k - a[i]];
  for (int i = 0; i <= n - 1; ++i) {
    double t = 0;
    for (int j = 0; j <= s; ++j)
      t += dp[i][j] *
           min((n * 1.0 / (n - i) + 1) * x / 2, (s - j) * 1.0 / (n - i));
    ans += t / C[i];
  }
  printf("%.12f\n", ans);
  return 0;
}
