#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  cin >> n >> l;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int m = 2 * max(a[0], l - a[n - 1]);
  for (int i = 1; i < n; i++) m = max(m, a[i] - a[i - 1]);
  cout << m / 2;
  if (m % 2)
    cout << ".5000000000" << endl;
  else
    cout << ".0000000000" << endl;
}
