#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m;
  double mx = 0.0;
  cin >> n >> m;
  long long a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  mx = 0;
  for (int i = 0; i < n - 1; i++) {
    if (a[i + 1] - a[i] > mx) mx = a[i + 1] - a[i];
  }
  double n1 = a[0];
  double n2 = m - a[n - 1];
  mx = mx / 2;
  double s = max(mx, max(n1, n2));
  printf("%.10f\n", s);
}
