#include <bits/stdc++.h>
using namespace std;
int read() {
  int s = 0, t = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') t = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') s = s * 10 + ch - '0', ch = getchar();
  return s * t;
}
double f[110][10010];
int a[110];
int main() {
  int n = read(), x = read(), sum = 0;
  double ans = 0;
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) sum += (a[i] = read());
  for (int i = 1; i <= n; i++)
    for (int j = i; j; j--)
      for (int k = a[i]; k <= sum; k++)
        f[j][k] += f[j - 1][k - a[i]] * j / (n - j + 1);
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= sum; j++) ans += f[i][j] * min((n + i) * x, j * 2) / i;
  printf("%.10lf\n", ans / 2);
  return 0;
}
