#include <bits/stdc++.h>
using namespace std;
int main(void) {
  int n, l;
  cin >> n >> l;
  int *arr = new int[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n);
  int d = max(arr[0] - 0, l - arr[n - 1]);
  d = 2 * d;
  for (int i = 0; i < n - 1; i++) {
    int diff = arr[i + 1] - arr[i];
    d = max(d, diff);
  }
  cout << setprecision(30) << d / 2.0;
  return 0;
}
