#include <bits/stdc++.h>
using namespace std;
double arr[100001];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, l;
  cin >> n >> l;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n);
  double maxI = -1.0;
  for (int i = 0; i < n - 1; i++) {
    maxI = max((arr[i + 1] - arr[i]) / 2, maxI);
  }
  cout << fixed << setprecision(9) << max(arr[0] - 0, max(maxI, l - arr[n - 1]))
       << "\n";
  return 0;
}
