#include <bits/stdc++.h>
using namespace std;
int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = (x << 3) + (x << 1) + (ch ^ 48);
    ch = getchar();
  }
  return x * f;
}
int n, sum, x, c[10005];
double f[105][10005], fac[10005];
double C(int x, int y) { return fac[x] / (fac[y] * fac[x - y]); }
int main() {
  n = read();
  x = read();
  fac[0] = 1;
  for (int i = 1; i <= n; i++)
    c[i] = read(), sum += c[i], fac[i] = fac[i - 1] * i * 1.0;
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    for (int j = n; j >= 1; j--) {
      for (int k = sum; k >= c[i]; k--) {
        f[j][k] = f[j][k] + f[j - 1][k - c[i]];
      }
    }
  }
  double ans = 0;
  for (int i = 0; i <= n - 1; i++) {
    for (int j = 0; j <= sum; j++) {
      ans += f[i][j] / C(n, i) *
             min((sum - j) * 1.0 / (n - i), (n * 1.0 / (n - i) + 1) * x / 2);
    }
  }
  printf("%.10lf\n", ans);
  return 0;
}
