#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  double l;
  cin >> n >> l;
  double a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  double diff = 0;
  for (int i = 1; i < n; i++) diff = max(diff, a[i] - a[i - 1]);
  double start = a[0] - 0, end = l - a[n - 1];
  double k = max(start, end);
  if (k >= diff / 2.0)
    cout << fixed << setprecision(10) << k;
  else
    cout << fixed << setprecision(10) << diff / 2.0;
}
