#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(0), cin.tie(0);
  int n, l;
  cin >> n >> l;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n);
  double maxy = INT_MIN * 1.0;
  for (int i = 0; i < n - 1; i++) {
    if (arr[i + 1] - arr[i] > maxy) maxy = arr[i + 1] - arr[i];
  }
  maxy *= 1.0;
  if (arr[0] == 0 or arr[n - 1] == l) {
    if (arr[0] == 0 and arr[n - 1] == l) {
      cout << fixed << setprecision(10) << maxy / 2;
    } else if (arr[0] == 0) {
      cout << fixed << setprecision(10) << max(maxy / 2, (l - arr[n - 1]) * 1.0)
           << "\n";
    } else {
      cout << fixed << setprecision(10) << max(maxy / 2, (arr[0]) * 1.0)
           << "\n";
    }
  } else {
    cout << fixed << setprecision(10)
         << max(maxy / 2, max(l - arr[n - 1], arr[0]) * 1.0) << "\n";
  }
  return 0;
}
