#include <bits/stdc++.h>
using namespace std;
const long long N = 1010;
long long n, l, seq[N];
long double ans;
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n >> l;
  for (long long i = 1; i <= n; ++i) cin >> seq[i];
  sort(seq + 1, seq + n + 1);
  ans = max((long double)seq[1], (long double)l - seq[n]);
  for (long long i = 1; i < n; ++i)
    ans = max(ans, ((long double)seq[i + 1] - seq[i]) / 2);
  cout << setprecision(9) << fixed;
  cout << ans << "\n";
  return 0;
}
