#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
using namespace std;
int32_t main() {
  long long n, l;
  cin >> n >> l;
  double a[n];
  for (long long i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  double mx = 0;
  for (long long i = 1; i < n; i++) mx = max(mx, a[i] - a[i - 1]);
  mx /= 2;
  if (mx < a[0]) mx = a[0];
  if (mx < l - a[n - 1]) mx = l - a[n - 1];
  cout << fixed << setprecision(12) << mx;
}
