#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l, i, j, k, arr[1004];
  cin >> n >> l;
  for (i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  double r, max;
  max = r = arr[0];
  for (i = 1; i < n; i++) {
    j = arr[i] - arr[i - 1];
    r = double(j) / 2;
    if (r > max) max = r;
  }
  r = l - arr[n - 1];
  if (r > max) max = r;
  printf("%.10lf\n", max);
  return 0;
}
