#include <bits/stdc++.h>
using namespace std;
int n, l;
int a[1005];
double ans;
int main() {
  scanf("%d%d", &n, &l);
  for (int i = 1; i <= n; ++i) scanf("%d", a + i);
  sort(a + 1, a + n + 1);
  a[n + 1] = l;
  for (int i = 1; i <= n - 1; ++i) ans = max(ans, (a[i + 1] - a[i]) / 2.0);
  ans = max(1.0 * a[1], ans);
  ans = max(1.0 * (l - a[n]), ans);
  cout << fixed << setprecision(10) << ans;
  return 0;
}
