#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l, i, j, s, ss;
  int a[1005];
  scanf("%d%d", &n, &l);
  for (i = 1; i <= n; i++) scanf("%d", &a[i]);
  sort(a + 1, a + n + 1);
  double ans = 0;
  s = 0;
  ss = a[1];
  if (l - a[n] > ss) ss = l - a[n];
  for (i = 1; i <= n - 1; i++)
    if (a[i] != a[i + 1] && a[i + 1] - a[i] > s) s = a[i + 1] - a[i];
  ans = (double)s / 2;
  if (ss > ans) ans = ss;
  printf("%.10lf\n", ans);
  return 0;
}
