#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, l, m = 0, c;
  double s, f, d, ans, e;
  cin >> n >> l;
  int a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  for (int i = 0; i < n - 1; i++) {
    if (a[i + 1] - a[i] > m) {
      m = a[i + 1] - a[i];
    }
  }
  d = a[0];
  f = (double)m / 2;
  s = max(d, f);
  e = l - a[n - 1];
  s = max(e, s);
  cout << fixed << setprecision(10) << s << endl;
}
