#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  int m = 0;
  cin >> n >> l;
  int ar[n];
  for (int i = 0; i < n; i++) {
    cin >> ar[i];
  }
  sort(ar, ar + n);
  for (int i = 0; i < n - 1; i++) {
    if (ar[i + 1] - ar[i] > m) {
      m = ar[i + 1] - ar[i];
    }
  }
  double x = ar[0];
  double y = (double)m / 2;
  double ans = max(x, y);
  double z = l - ar[n - 1];
  ans = max(z, ans);
  cout << fixed << setprecision(10) << ans;
}
