#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int l;
  cin >> n >> l;
  int arr[n];
  for (int i = 0; i < n; i++) cin >> arr[i];
  int temp;
  for (int p = 0; p < n - 1; p++) {
    for (int q = p + 1; q < n; q++) {
      if (arr[p] > arr[q]) {
        temp = arr[p];
        arr[p] = arr[q];
        arr[q] = temp;
      }
    }
  }
  int maximum_gap = arr[0];
  for (int p = 1; p < n; p++) {
    if ((arr[p] - arr[p - 1]) > maximum_gap) maximum_gap = arr[p] - arr[p - 1];
  }
  int a = arr[0];
  int b = l - arr[n - 1];
  if (maximum_gap / 2.0 >= a && maximum_gap / 2.0 >= b)
    printf("%.9f", maximum_gap / 2.0);
  else if (b > a)
    printf("%.9f", (float)b);
  else
    printf("%.9f", (float)a);
  return 0;
}
