#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);
  double max = 0;
  int b = a[0];
  for (int i = 1; i < n; i++) {
    if (a[i] - b > max) max = a[i] - b;
    b = a[i];
  }
  max /= 2;
  if (a[0] > max) max = a[0];
  if (l - a[n - 1] > max) max = l - a[n - 1];
  printf("%.10f\n", max);
  return 0;
}
