#include <bits/stdc++.h>
using namespace std;
const int N = 110, M = 10010;
int n;
long double x;
int c[N], all;
long double binom[N][N];
long double f[N][M];
int main() {
  cin >> n >> x;
  for (int i = 1; i <= n; i++) scanf("%d", &c[i]), all += c[i];
  f[0][0] = 1;
  for (int i = 0; i <= n; i++) {
    binom[i][0] = binom[i][i] = 1;
    for (int j = 1; j < i; j++)
      binom[i][j] = binom[i - 1][j] + binom[i - 1][j - 1];
  }
  f[0][0] = 1;
  for (int id = 1; id <= n; id++) {
    for (int i = id; i; i--) {
      for (int j = all; j >= c[id]; j--) {
        f[i][j] += f[i - 1][j - c[id]];
      }
    }
  }
  long double ans = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= all; j++) {
      long double v = f[i][j];
      v /= binom[n][i];
      v *= min(x / 2 + x / 2 * n / i, (long double)j / (long double)i);
      ans += v;
    }
  }
  printf("%.15Lf\n", ans);
}
