#include <bits/stdc++.h>
using namespace std;
int n, l;
double d;
double arr[1001];
int main() {
  cin >> n >> l;
  for (int i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  d = 0;
  for (int i = 0; i < n - 1; i++) d = max(d, arr[i + 1] - arr[i]);
  cout << fixed << setprecision(9) << max(d / 2, max(arr[0], l - arr[n - 1]));
}
