#include <bits/stdc++.h>
using namespace std;
double a[1005];
vector<double> v;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  vector<double> v1;
  long long n, l;
  cin >> n >> l;
  for (long long i = 0; i < n; ++i) cin >> a[i];
  if (n == 1) {
    double m = max(a[0], l - a[0]);
    cout << fixed;
    cout << setprecision(10) << m;
    return 0;
  }
  sort(a, a + n);
  for (long long i = 1; i < n; ++i) v.push_back(a[i] - a[i - 1]);
  auto maxx = max_element(v.begin(), v.end());
  v1.push_back((*maxx) / 2);
  v1.push_back(a[0] - 0);
  v1.push_back(l - a[n - 1]);
  maxx = max_element(v1.begin(), v1.end());
  cout << fixed;
  cout << setprecision(10) << *maxx;
  return 0;
}
