#include <bits/stdc++.h>
const int N = 105;
const int M = 1e5 + 5;
using namespace std;
int c[N];
double f[N][M], ans = 0;
;
int main() {
  int n, x, sum = 0;
  scanf("%d%d", &n, &x);
  for (int i = (1); i <= (n); ++i) scanf("%d", &c[i]), sum += c[i];
  f[0][0] = 1;
  for (int i = (1); i <= (n); ++i)
    for (int j = (n); j >= (1); --j)
      for (int k = (0); k <= (sum - c[i]); ++k)
        f[j][k + c[i]] += (double)f[j - 1][k] * j / (n - j + 1);
  for (int i = (0); i <= (n - 1); ++i)
    for (int j = (0); j <= (sum); ++j)
      ans += (double)f[i][j] * min((double)(n + n - i) * x, 2.0 * (sum - j)) /
             (n - i);
  printf("%.10f", ans / 2.0);
}
