#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l, a[1000], t = 0;
  double m, x;
  cin >> n >> l;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  m = max(a[0], l - a[n - 1]), m *= 2;
  for (int i = 0; i < n - 1; i++) {
    x = a[i + 1] - a[i];
    if (x > m) m = x, t = 1;
  }
  printf("%.10f\n", m / 2);
  return 0;
}
