#include <bits/stdc++.h>
using namespace std;
const int MAXN = 105;
const int MAXC = 10005;
int c[MAXN];
double f[MAXN][MAXC];
int main() {
  int n, s = 0;
  double x;
  scanf("%d%lf", &n, &x);
  x /= 2;
  for (int i = 1; i <= n; i++) scanf("%d", &c[i]), s += c[i];
  f[0][0] = 1;
  for (int i = 1; i <= n; i++)
    for (int j = n; j >= 1; j--)
      for (int k = c[i]; k <= s; k++)
        f[j][k] += f[j - 1][k - c[i]] / (n - j + 1) * j;
  double ans = 0;
  for (int i = 1; i <= n; i++)
    for (int j = 0; j <= s; j++)
      ans += f[i][j] * min((double)j / i, ((double)n / i + 1) * x);
  printf("%.10lf\n", ans);
  return 0;
}
