#include <bits/stdc++.h>
using namespace std;
const int maxn = 110, maxv = 10010;
long double dp[maxn][maxv];
int c[maxn];
int main() {
  int n, x;
  scanf("%d %d", &n, &x);
  int sum = 0;
  for (int i = 1; i <= n; i++) scanf("%d", c + i), sum += c[i];
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++)
    for (int j = i; j; j--)
      for (int k = c[i]; k <= sum; k++)
        dp[j][k] += dp[j - 1][k - c[i]] * j / (long double)(n - j + 1);
  long double ans = 0;
  for (int i = 1; i <= n; i++)
    for (int j = 0; j <= sum; j++)
      ans += dp[i][j] * min((long double)j / i,
                            (long double)x / 2 * ((long double)n / i + 1));
  printf("%.10Lf\n", ans);
  return 0;
}
