#include <bits/stdc++.h>
using namespace std;
int main() {
  int a[1002], l, n;
  scanf("%d %d", &n, &l);
  for (int i = 0; i < n; i++) scanf("%d", a + i);
  sort(a, a + n);
  double d = max(a[0] - 0, l - a[n - 1]);
  for (int i = n - 1; i > 0; i--) d = max(d, double(a[i] - a[i - 1]) / 2);
  printf("%0.10lf", d);
}
