#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  cin >> n >> l;
  int a[n];
  int zero = 0, len = 0;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] == 0)
      zero = 1;
    else if (a[i] == l)
      len = 1;
  }
  sort(a, a + n);
  int mx = 0;
  for (int i = 0; i < n - 1; i++) mx = max(mx, a[i + 1] - a[i]);
  if (!zero) mx = max(mx, 2 * (a[0] - 0));
  if (!len) mx = max(mx, 2 * (l - a[n - 1]));
  cout << setprecision(9) << fixed << mx / 2.0;
  return 0;
}
