#include <bits/stdc++.h>
using namespace std;
long double comb[110][110], d[110][10010];
int v[110];
int main() {
  int n, x, sum = 0;
  scanf("%d%d", &n, &x);
  comb[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    comb[i][0] = 1;
    for (int j = 1; j <= i; j++)
      comb[i][j] = comb[i - 1][j - 1] + comb[i - 1][j];
  }
  for (int i = 1; i <= n; i++) {
    scanf("%d", &v[i]);
    sum += v[i];
  }
  d[0][0] = 1;
  for (int i = 1; i <= n; i++)
    for (int j = n; j > 0; j--)
      for (int k = v[i]; k <= sum; k++) d[j][k] += d[j - 1][k - v[i]];
  long double ans = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j <= sum; j++)
      ans += (d[i][j] / comb[n][i]) *
             min(1.0 * (sum - j) / (n - i),
                 (1.0 * ((1.0 * n / (n - i)) + 1.0) * x) / 2);
  printf("%.12f", (double)ans);
  return 0;
}
