#include <bits/stdc++.h>
using namespace std;
int main() {
  double ans = 0;
  double x = -200;
  int n;
  double l;
  cin >> n >> l;
  double a[n + 5];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  for (int i = 1; i < n; i++) {
    ans = max((a[i] - a[i - 1]), x);
    x = ans;
  }
  ans /= 2;
  double k = max(a[0], l - a[n - 1]);
  if (k > ans) {
    ans = k;
  }
  cout.precision(9);
  cout << fixed << ans;
}
