#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int x = 0;
  bool f = 0;
  char ch = getchar();
  for (; !isdigit(ch); ch = getchar()) f = (ch == '-');
  for (; isdigit(ch); ch = getchar()) x = (x << 3) + (x << 1) + (ch ^ 48);
  return f ? -x : x;
}
const int N = 109;
const int M = 1e4 + 9;
int n, x, sum, c[N];
double f[N][M], ans;
int main() {
  n = read();
  x = read();
  f[0][0] = 1;
  for (int i = 1; i <= n; ++i) c[i] = read(), sum += c[i];
  for (int i = 1; i <= n; ++i)
    for (int j = i - 1; ~j; --j)
      for (int v = 0; v < sum; ++v)
        if (f[j][v]) f[j + 1][v + c[i]] += f[j][v] * (j + 1) / (n - j);
  for (int i = 0; i < n; ++i)
    for (int v = 0; v < sum; ++v)
      if (f[i][v])
        ans += f[i][v] *
               min((1.0 * n / (n - i) + 1) * x / 2, 1.0 * (sum - v) / (n - i));
  printf("%.17lf\n", ans);
  return 0;
}
