#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  int n, l;
  cin >> n >> l;
  vector<int> a;
  for (int i = 1; i <= n; i++) {
    int x;
    cin >> x;
    a.push_back(x);
  }
  sort(a.begin(), a.end());
  int ans = max(a[0] * 2, (l - a[a.size() - 1]) * 2);
  for (int i = 1; i < a.size(); i++) ans = max(ans, a[i] - a[i - 1]);
  long double ret = (long double)ans / 2;
  cout << std::fixed << setprecision(9) << ret;
  return 0;
}
