#include <bits/stdc++.h>
using namespace std;
const int N = 105;
int a[N], n;
double x, ans, dp[N][N * N], c[N][N];
int main() {
  scanf("%d%lf", &n, &x);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]), ans += a[i];
  dp[0][0] = c[0][0] = 1;
  for (int i = 1; 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];
  }
  for (int i = 1; i <= n; i++)
    for (int j = i; j; j--)
      for (int k = 10000; k >= a[i]; k--) dp[j][k] += dp[j - 1][k - a[i]];
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= 10000; j++) {
      double vv = x + x / 2 * ((double)n / i - 1) - (double)j / i;
      if (vv < 0) ans += vv * dp[i][j] / c[n][i];
    }
  printf("%.10lf\n", ans);
}
