#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  double l;
  cin >> n >> l;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int max = a[0] - 0;
  for (int i = 1; i < n; i++) {
    if (a[i] - a[i - 1] > max) max = a[i] - a[i - 1];
  }
  cout << fixed;
  cout << std::setprecision(10);
  double r = 0.0;
  r = double(max / 2.0);
  if (r < a[0] - 0.0 || r < double(l) - double(a[n - 1])) {
    if (a[0] - 0 > double(l) - double(a[n - 1]))
      r = a[0] - 0;
    else
      r = double(l) - double(a[n - 1]);
  }
  cout << double(r) << endl;
  return 0;
}
