#include <bits/stdc++.h>
using namespace std;
const long long inf = 0;
const long double eps = 0;
const long long ms = 0;
const long long md = 0;
int main() {
  ios::sync_with_stdio(false);
  long long n, l;
  cin >> n >> l;
  vector<long long> a(n, 0);
  for (long long i = 0; i < n; i++) cin >> a[i];
  sort(a.begin(), a.end());
  long long maxdif = 0;
  for (long long i = 1; i < n; i++) maxdif = max(maxdif, a[i] - a[i - 1]);
  long double rear = l - a[n - 1];
  long double front = a[0];
  long double inbet = double(maxdif) / 2.0;
  cout << fixed << max(max(rear, front), inbet) << endl;
  return 0;
}
