#include <bits/stdc++.h>
using namespace std;
long double C[123][123];
long double dp[123][12345];
int a[123];
int main() {
  int n, x;
  cin >> n >> x;
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    sum += a[i];
  }
  C[0][0] = 1;
  for (int i = 1; i <= 120; i++) {
    C[i][0] = 1;
    for (int j = 1; j <= i; j++) {
      C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
    }
  }
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    for (int j = n; j >= 1; --j) {
      for (int k = a[i]; k <= sum; k++) {
        dp[j][k] = dp[j][k] + dp[j - 1][k - a[i]];
      }
    }
  }
  cerr << "finished" << endl;
  long double ans = 0.0;
  for (int k = 1; k <= n; k++) {
    for (int s = 1; s <= sum; s++) {
      ans += 1.0 * dp[k][s] / C[n][k] *
             min(1.0 * s / k, (1.0 * (n + k) / k) * x * 0.5);
    }
  }
  printf("%.9Lf\n", ans);
  return 0;
}
