#include <bits/stdc++.h>
using namespace std;
double dmax(double a, double b);
void solve();
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
  return 0;
}
double dmax(double a, double b) {
  if (a > b) return a;
  return b;
}
void solve() {
  int n, l;
  cin >> n >> l;
  int arr[n];
  for (int i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  double d = dmax(arr[0] / 1.0, (l - arr[n - 1]) / 1.0);
  for (int i = 1; i < n; i++)
    if ((arr[i] - arr[i - 1]) / 2.0 > d) d = (arr[i] - arr[i - 1]) / 2.0;
  cout << setprecision(10);
  cout << d << "\n";
}
