#include <bits/stdc++.h>
using namespace std;
const int dl = 10069;
void bib() {
  for (int i = 0; i < (int)10; i++) {
    cout << "\a";
  }
}
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);
  double max = 0;
  for (int i = 0; i + 1 < n; i++) {
    if (a[i + 1] - a[i] > max) {
      max = a[i + 1] - a[i];
    }
  }
  max /= 2;
  if (a[0] > max) {
    max = a[0];
  }
  if (l - a[n - 1] > max) {
    max = l - a[n - 1];
  }
  cout.precision(10);
  cout << fixed << max;
  return 0;
}
