#include <bits/stdc++.h>
const int N = 105;
double p[N], f[105][10005];
int sum, x, n, v;
double C(int x, int y) { return p[x] / (p[y] * p[x - y]); }
int main() {
  scanf("%d%d", &n, &v);
  p[0] = 1;
  for (int i = 1; i <= n; i++) p[i] = p[i - 1] * i;
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    scanf("%d", &x);
    sum += x;
    for (int ct = i; ct >= 1; ct--)
      for (int j = sum; j >= x; j--) f[ct][j] += f[ct - 1][j - x];
  }
  double ans = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j <= sum; j++)
      if (f[i][j])
        ans = ans + f[i][j] / C(n, i) *
                        std::min((sum - j) * 1.0 / (n - i),
                                 (n * 1.0 / (n - i) + 1) * v / 2);
  printf("%.10lf\n", ans);
}
