#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  cin >> n >> l;
  double a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(&a[0], &a[n]);
  float x = a[0] - 0;
  float y = l - a[n - 1];
  for (int i = 0; i < n - 1; i++) a[i] = (a[i + 1] - a[i]) / 2;
  if (x > y)
    a[n - 1] = x;
  else
    a[n - 1] = y;
  sort(&a[0], &a[n]);
  cout << std::fixed << a[n - 1];
}
