#include <bits/stdc++.h>
using namespace std;
int n, x, a[110], sum = 0;
double f[110][10010], ans = 0;
int main() {
  scanf("%d%d", &n, &x);
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    sum += a[i];
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i; j; j--) {
      for (int k = a[i]; k <= sum; k++) {
        f[j][k] += f[j - 1][k - a[i]] * j / (n - j + 1);
      }
    }
  }
  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);
}
