#include <bits/stdc++.h>
using namespace std;
vector<long long int> v;
int main() {
  long long int n, a, l;
  cin >> n >> l;
  for (int i = 0; i < n; i++) {
    cin >> a;
    v.push_back(a);
  }
  sort(v.begin(), v.end());
  int max = 0;
  for (int i = 1; i < v.size(); i++) {
    if (v[i] - v[i - 1] > max) max = v[i] - v[i - 1];
  }
  double d = max;
  d = d / 2;
  if (v[0] - 0 > d) {
    max = v[0] - 0;
    d = v[0] - 0;
  }
  if (l - v[v.size() - 1] > d) {
    max = l - v[v.size() - 1];
    d = max;
  }
  cout << setprecision(9) << d << endl;
  return 0;
}
