#include <bits/stdc++.h>
using namespace std;
const int N = 120, M = 10020;
int n, x, a[N];
double f[N][M];
int main() {
  scanf("%d%d", &n, &x);
  int sum = 0;
  for (int i = 1; i <= n; ++i) scanf("%d", &a[i]), sum += a[i];
  f[0][0] = 1;
  for (int i = 1; i <= n; ++i)
    for (int j = i; j >= 1; --j)
      for (int k = a[i]; k <= sum; ++k)
        f[j][k] += f[j - 1][k - a[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, j * 2) / i;
  printf("%.10lf", ans / 2);
  return 0;
}
