#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  cin >> n >> l;
  int a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  int maxx = 0;
  for (int i = 1; i < n; i++) {
    maxx = max(maxx, a[i] - a[i - 1]);
  }
  double ans = ((double)(maxx)) / 2;
  double minn = (double)(*min_element(a, a + n));
  ans = max(ans, minn);
  double maxi = (double)(*max_element(a, a + n));
  ans = max(ans, l - maxi);
  printf("%0.9lf", ans);
  printf("\n");
  return 0;
}
