#include <bits/stdc++.h>
using namespace std;
int a[1010];
int main() {
  int n, l, ans;
  scanf("%d%d", &n, &l);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  sort(a + 1, a + n + 1);
  ans = max(l - a[n], a[1]) * 2;
  for (int i = 2; i <= n; i++) ans = max(ans, a[i] - a[i - 1]);
  printf("%.10f", ans / 2.0);
  return 0;
}
