#include <bits/stdc++.h>
using namespace std;
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
long long lcm(long long a, long long b) { return a * b / gcd(a, b); }
int32_t main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  long long n, l;
  cin >> n >> l;
  vector<long long> a(n);
  for (long long &i : a) cin >> i;
  sort(a.begin(), a.end());
  double ans = a[0];
  for (long long i = 0; i < n - 1; i++) {
    long long d = a[i + 1] - a[i];
    ans = max(ans, (double)d / 2);
  }
  ans = max(ans, (double)(l - a[n - 1]));
  cout << fixed << setprecision(10) << ans << '\n';
  return 0;
}
