#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 5, M = 1e6 + 6, OO = 0x3f3f3f3f;
int n, l, arr[N];
double diff[N], mx = 0;
int main() {
  scanf("%d %d", &n, &l);
  for (int i = 0; i < n; ++i) scanf("%d", &arr[i]);
  sort(arr, arr + n);
  for (int i = 1; i < n; ++i) {
    diff[i] = (arr[i] - arr[i - 1]) / (2.0);
    if (diff[i] > mx) mx = diff[i];
  }
  mx = max(mx, arr[0] * 1.0);
  if (l > arr[n - 1]) mx = max(mx, (l - arr[n - 1]) * 1.0);
  printf("%.10lf", mx);
  return 0;
}
