#include <bits/stdc++.h>
using namespace std;
int main() {
  ;
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n, l, A[2000];
  cin >> n >> l;
  for (int i = 0; i < n; i++) cin >> A[i];
  sort(A, A + n);
  double ans = 0.0;
  for (int i = 0; i < n - 1; i++) {
    ans = max(ans, ((1.0 * A[i + 1] - A[i]) / 2));
  }
  ans = max(ans, 1.0 * (l - A[n - 1]));
  ans = max(ans, 1.0 * A[0]);
  cout << setprecision(9) << fixed;
  cout << ans;
}
