#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l, a[1002] = {0};
  cin >> n >> l;
  for (int i = 1; i <= n; i++) cin >> a[i];
  sort(a + 1, a + n + 1);
  double mx = 0;
  for (int i = 1; i <= n; i++)
    if (mx < a[i + 1] - a[i]) {
      mx = a[i + 1] - a[i];
    }
  mx = mx / 2;
  if (a[1] == 0 && a[n] == l) {
    cout << setprecision(10) << mx;
    return 0;
  } else {
    if (a[1] == 0) {
      if (l - a[n] > mx) mx = l - a[n];
    }
    if (a[n] == l) {
      if (a[1] > mx) mx = a[1];
    }
    if (a[1] != 0 && a[n] != l) {
      if (a[1] > mx) mx = a[1];
      if (l - a[n] > mx) mx = l - a[n];
    }
  }
  cout << setprecision(10) << mx;
  return 0;
}
