#include <bits/stdc++.h>
using namespace std;
int n;
int X, c[110];
double dp[110][10010];
double C[110][110];
int main() {
  scanf("%d%d", &n, &X);
  for (int i = 1; i <= n; i++) scanf("%d", c + i);
  dp[0][0] = 1;
  int S = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = i - 1; j >= 0; j--)
      for (int k = 0; k <= S; k++) dp[j + 1][k + c[i]] += dp[j][k];
    S += c[i];
  }
  for (int i = 0; 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 = 1; i <= n; i++)
    for (int j = 1; j <= S; j++)
      ans += dp[i][j] / C[n][i] * min((1.0 * n / i + 1) * X / 2, 1.0 * j / i);
  printf("%.11lf\n", ans);
  return 0;
}
