#include <bits/stdc++.h>
using namespace std;
using vi = vector<int>;
using ll = long long;
using vl = vector<ll>;
using pi = pair<int, int>;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  ;
  int n, l;
  cin >> n >> l;
  vi a(n);
  for (auto &e : a) cin >> e;
  int mx = 0;
  sort((a).begin(), (a).end());
  for (int i = 1; i < n; i++) {
    mx = max(mx, a[i] - a[i - 1]);
  }
  cout << std::fixed << setprecision(20)
       << max({(double)mx / 2.0, double(a[0]), (double)l - a.back()});
  return 0;
}
