#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cout << setprecision(9) << fixed;
  int n, l;
  cin >> n >> l;
  vector<double> a(n);
  for (double& e : a) cin >> e;
  sort(a.begin(), a.end());
  double diff = 0;
  for (int i = 1; i < n; ++i) {
    diff = max(diff, a[i] - a[i - 1]);
  }
  cout << max(diff / 2, max(a.front() - 0, l - a.back())) << '\n';
  return 0;
}
