#include <bits/stdc++.h>
using namespace std;
const int oo = 1000000009;
const double eps = 1e-6;
const int mod = 1000000007;
const int mx = 1013;
int a[mx], n, l;
int main() {
  scanf("%d %d", &n, &l);
  for (int i = 0; i < (n); ++i) scanf("%d", a + i);
  sort(a, a + n);
  double ans = 0;
  for (int i = 1; i < (n); ++i) ans = max(ans, (a[i] - a[i - 1]) / 2.0);
  ans = max(ans, 1.0 * max(a[0], l - a[n - 1]));
  printf("%.01lf\n", ans);
  return 0;
}
