#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 3;
int n, l;
double ans, a[N];
int main() {
  scanf("%d %d", &n, &l);
  for (int i = 0; i < n; ++i) scanf("%lf", a + i);
  sort(a, a + n);
  if (a[0] != 0) ans = a[0];
  if (a[n - 1] != l) ans = max(ans, l - a[n - 1]);
  for (int i = 0; i < n - 1; ++i) {
    ans = max(ans, (a[i + 1] - a[i]) / 2);
  }
  printf("%.10lf\n", ans);
}
