#include <bits/stdc++.h>
using namespace std;
using namespace std;
int main() {
  long long n, l;
  cin >> n >> l;
  vector<long long> vec;
  for (long long i = 0; i < n; i++) {
    long long t;
    cin >> t;
    vec.push_back(t);
  }
  sort(vec.begin(), vec.end());
  double mix = abs(0 - vec[0]);
  for (long long i = 1; i < n; i++) {
    if (abs(vec[i] - vec[i - 1]) > mix) mix = abs(vec[i] - vec[i - 1]);
  }
  mix = mix / 2;
  double mixx = max(vec[0], (l - vec[vec.size() - 1]));
  cout.precision(17);
  cout << fixed << max(mix, mixx);
}
