#include <bits/stdc++.h>
using namespace std;
template <typename T>
void read(T &a) {
  T x = 0, f = 1;
  register char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = (x << 1) + (x << 3) + (ch ^ 48);
    ch = getchar();
  }
  a = x * f;
}
template <typename T>
void write(T x) {
  if (x < 0) putchar('-'), x = -x;
  if (x < 10) return (void)putchar(x + '0');
  write(x / 10);
  putchar(x % 10 + '0');
}
template <typename T>
void writeln(T x) {
  write(x);
  putchar('\n');
}
template <typename T>
void writes(T x) {
  write(x);
  putchar(' ');
}
template <typename T, typename... Args>
void read(T &t, Args &...args) {
  read(t);
  read(args...);
}
template <typename T, typename... Args>
void writes(T t, Args... args) {
  writes(t);
  writes(args...);
}
template <typename T, typename... Args>
void writeln(T t, Args... args) {
  writes(t);
  writes(args...);
  putchar('\n');
}
long long n, x, a[105];
long double dp[105][10005];
signed main() {
  read(n, x);
  long long sum = 0;
  dp[0][0] = 1;
  for (long long i = 1; i <= n; i++) {
    read(a[i]);
    sum += a[i];
    for (long long j = i; j >= 1; j--)
      for (long long k = sum; k >= a[i]; k--)
        dp[j][k] += dp[j - 1][k - a[i]] * j / (n - j + 1);
  }
  long double ans = 0;
  for (long long i = 1; i <= n; i++)
    for (long long j = 0; j <= sum; j++)
      ans += min((n + i) / 2.0 * x, (double)j) * dp[i][j] / i;
  printf("%.10Lf\n", ans);
  return 0;
}
