#include <bits/stdc++.h>
int main() {
  short n;
  unsigned long long l;
  double dif;
  scanf("%hd %llu", &n, &l);
  unsigned long long arr[n];
  for (int i = 0; i < n; i++) scanf("%llu", &arr[i]);
  std::sort(arr, arr + n);
  dif = arr[0];
  for (int i = 1; i < n; i++) {
    if (((arr[i] - arr[i - 1]) * 1.0) / 2 > dif)
      dif = ((arr[i] - arr[i - 1]) * 1.0) / 2;
  }
  dif = dif < l - arr[n - 1] ? l - arr[n - 1] : dif;
  printf("%.10f", dif);
  return 0;
}
