#include <bits/stdc++.h>
using namespace std;
int main() {
  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);
  double maxDiff = arr[0], tempDiff;
  for (int i = 0; i < n - 1; i++) {
    tempDiff = abs(arr[i] - arr[i + 1]) / 2.0;
    if (maxDiff < tempDiff) maxDiff = tempDiff;
  }
  int lastDiff = (double)l - arr[n - 1];
  if (lastDiff > maxDiff) maxDiff = lastDiff;
  printf("%.3f000000", maxDiff);
  return 0;
}
