#include <bits/stdc++.h>
using namespace std;
void read(int &x) {
  x = 0;
  int f = 1;
  char ch = getchar();
  for (; !isdigit(ch); ch = getchar())
    if (ch == '-') f = -f;
  for (; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
  x *= f;
}
void print(int x) {
  if (x < 0) putchar('-'), x = -x;
  if (!x) return;
  print(x / 10), putchar(x % 10 + 48);
}
void write(int x) {
  if (!x)
    putchar('0');
  else
    print(x);
  putchar('\n');
}
const int maxn = 1e6 + 10;
const int inf = 1e9;
const double eps = 1e-8;
const int mod = 1e9 + 7;
double f[102][10002], c[102][102];
int n, a[maxn], x;
int main() {
  read(n), read(x);
  int s = 0;
  for (int i = 1; i <= n; i++) read(a[i]), s += a[i];
  f[0][0] = c[0][0] = 1;
  for (int i = 1; i <= n; i++)
    for (int j = i; ~j; j--)
      for (int k = 0; k <= s; k++)
        f[j][k] = f[j][k] + (k >= a[i] && j ? f[j - 1][k - a[i]] : 0);
  for (int i = 1; i <= n; i++) {
    c[i][0] = 1;
    for (int j = 1; j <= i; j++) c[i][j] = c[i - 1][j] + c[i - 1][j - 1];
  }
  double ans = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < s; j++)
      ans +=
          1.0 * f[i][j] / c[n][i] *
          min(1.0 * (s - j) / (n - i), 1.0 * (1.0 * n / (n - i) + 1) * x / 2);
  printf("%.10lf\n", ans);
  return 0;
}
