#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int n, l;
  cin >> n >> l;
  vector<int> v(n);
  for (long long i = (0); i < (n); ++i) {
    cin >> v[i];
  }
  double ans = 0.0;
  sort(v.begin(), v.end());
  vector<int> gaps;
  for (long long i = (0); i < (v.size() - 1); ++i) {
    gaps.push_back(v[i + 1] - v[i]);
  }
  double min = max(v[0] * 1.0, l - v.back() * 1.0);
  for (int i : gaps) {
    min = max(min, i * 1.0 / 2.0);
  }
  printf("%.12f\n", min);
  return 0;
}
