#include <bits/stdc++.h>
using namespace std;
int main() {
  int check0 = 0, checkl = 0;
  double n, l, i, j, ans = 0;
  cin >> n >> l;
  vector<long long> a(n);
  for (i = 0; i < n; i++) cin >> a[i];
  sort(a.begin(), a.end());
  for (i = 0; i < n; i++) {
    if (a[i] == 0)
      check0 = 1;
    else if (a[i] == l)
      checkl = 1;
    if (i > 0) {
      if ((a[i] - a[i - 1]) > ans) ans = a[i] - a[i - 1];
    }
  }
  ans /= 2;
  if (!check0)
    if (a[0] > ans) ans = a[0];
  if (!checkl)
    if (l - a[n - 1] > ans) ans = l - a[n - 1];
  cout << setprecision(10) << ans;
  return 0;
}
