#include <bits/stdc++.h>
using namespace std;
int n, x, sum;
int a[105];
double dp[105][10005], ans;
int main() {
  scanf("%d%d", &n, &x);
  dp[0][0] = 1;
  for (int i = 1; i <= n; ++i) scanf("%d", &a[i]), sum += a[i];
  for (int i = 1; i <= n; ++i)
    for (int j = n - 1; ~j; --j)
      for (int k = 0; k <= sum - a[i]; ++k)
        dp[j + 1][k + a[i]] += dp[j][k] * (j + 1) / (n - j);
  for (int i = 1; i <= n; ++i)
    for (int j = 0; j <= sum; ++j)
      ans += dp[i][j] * min(1.0 * j / i, (1.0 * n / i + 1) * x * 0.5);
  printf("%.12lf\n", ans);
}
