#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i, l, arr[1005], m;
  cin >> n >> l;
  for (i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  m = max(arr[0], l - arr[n - 1]) * 2;
  for (i = 1; i < n; i++) m = max(m, arr[i] - arr[i - 1]);
  cout << setprecision(10) << m / 2.0 << endl;
}
