#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  long long n;
  double d, ans = 0, l;
  cout << setprecision(10) << fixed;
  cin >> n >> l;
  vector<double> a(n);
  for (long long i = 0; i < n; i++) cin >> a[i];
  sort(a.begin(), a.end());
  for (long long i = 1; i < n; i++) {
    d = a[i] - a[i - 1];
    ans = max(ans, d / 2);
  }
  ans = max(ans, a[0]);
  ans = max(ans, l - a[n - 1]);
  cout << ans << '\n';
  return 0;
}
