#include <bits/stdc++.h>
using namespace std;
const int N = 2100;
const long long mod = 1e9 + 7;
int n, x;
int a[N], b[N];
double f[110][11000];
int sum;
double ans;
const double eps = 1e-12;
double cost[110];
int d[N];
int main() {
  scanf("%d %d", &n, &x);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++) d[i] = a[i] - x, sum += d[i];
  for (int i = 1; i <= n; i++) {
    double extra = (double)(i - 1) / (double)(n - i + 1) * x / 2.0;
    ans += extra + x;
  }
  for (int i = 1; i <= n; i++) {
    double extra = (double)(n - i) / double(i) * x / 2.0;
    cost[i] = cost[i - 1] + extra + x;
  }
  f[0][sum] = 1.0;
  for (int i = 1; i <= n; i++)
    for (int j = n - 1; j >= 0; j--)
      for (int k = 0; k <= sum; k++) {
        double p = f[j][k] / (double)(n - j) * (j + 1);
        f[j + 1][k - d[i]] += p;
      }
  for (int j = 0; j < n; j++)
    for (int k = 0; k <= sum; k++)
      if (f[j][k] > eps && j * x >= 2 * k) {
        ans -= f[j][k] * ((double)x / 2.0 * (double)j / (double)(n - j) -
                          (double)k / (double)(n - j));
      }
  printf("%.20f\n", ans);
  return 0;
}
