#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  cin >> n >> l;
  double a[n + 1];
  double Z = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  sort(a + 1, a + n + 1);
  for (int i = 2; i <= n; i++) {
    Z = max(a[i] - a[i - 1], Z);
  }
  double last = l - a[n];
  double first = a[1];
  cout << fixed << setprecision(10) << max({first, last, Z / 2}) << endl;
}
