#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l, A[1001];
  double mxdst = 0, ans = 0;
  cin >> n >> l;
  for (int i = 0; i < n; i++) cin >> A[i];
  sort(A, A + n);
  for (int i = 0; i < n - 1; i++) {
    mxdst = max(mxdst, (double)A[i + 1] - A[i]);
  }
  ans = max(mxdst / 2, max((double)A[0] - 0, (double)l - A[n - 1]));
  printf("%0.10lf\n", ans);
  return 0;
}
