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