#include <bits/stdc++.h>
using namespace std;
double dp[101][10001];
int a[101];
int n;
int x, sum;
double ans;
int main() {
  scanf("%d %d", &n, &x);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    sum += a[i];
  }
  dp[0][0] = 1.0;
  for (int i = 1; i <= n; i++) {
    for (int j = i; j >= 1; j--) {
      for (int k = a[i]; k <= sum; k++) {
        dp[j][k] += dp[j - 1][k - a[i]] * j / (n - j + 1);
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= sum; j++) {
      ans += dp[i][j] * (double)min(x * (i + n), 2 * j) / i;
    }
  }
  printf("%.10lf", ans / 2);
  return 0;
}
