#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, l;
  double mn = 0;
  double mx = 0;
  cin >> n >> l;
  long *arr = new long[n + 2];
  arr[0] = 0;
  arr[n + 1] = l;
  for (int i = 1; i < n + 1; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n + 2);
  mx = max(arr[1] - arr[0], arr[n + 1] - arr[n]);
  for (int i = 1; i < n; i++) {
    if (arr[i + 1] - arr[i] > mx * 2 && arr[i + 1] - arr[i] > mn) {
      mn = arr[i + 1] - arr[i];
    }
  }
  if (mn > mx) {
    cout << fixed;
    cout << setprecision(9) << mn / 2;
  } else {
    cout << fixed;
    cout << setprecision(9) << mx;
  }
  return 0;
}
