#include <bits/stdc++.h>
using namespace std;
int n, l, k, i, j;
int numbers[1005];
double ad, bd, cd;
int main() {
  scanf("%d %d", &n, &l);
  for (i = 0; i < n; i++) {
    scanf("%d", &numbers[i]);
  }
  sort(numbers, numbers + n);
  ad = numbers[0];
  for (i = 0; i < n - 1; i++) {
    bd = max(bd, double(double((numbers[i + 1] - numbers[i])) / 2));
  }
  cd = l - numbers[n - 1];
  printf("%f\n", max({ad, bd, cd}));
  return 0;
}
