#include <bits/stdc++.h>
using namespace std;
double f[105][10005], c[105][105];
int a[105];
double minn(double x, double y) {
  if (x < y) return x;
  return y;
}
int main() {
  int n, sum = 0;
  double X;
  cin >> n >> X;
  for (int i = 0; i <= n; i++) c[i][0] = 1;
  for (int i = 1; i <= n; i++) {
    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++) scanf("%d", &a[i]), sum += a[i];
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    for (int j = i; j; j--) {
      for (int k = a[i]; k <= sum; k++) {
        f[j][k] += f[j - 1][k - a[i]];
      }
    }
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= sum; j++) f[i][j] /= c[n][i];
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= sum; j++) {
      ans += f[i][j] * minn((n + i) * X * 1.0, j * 2.0) / i;
    }
  }
  printf("%.10lf\n", ans / 2.0);
  return 0;
}
