#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, l, input;
  vector<long long> a;
  cin >> n >> l;
  for (long long i = 0; i < n; i++) {
    cin >> input;
    a.push_back(input);
  }
  sort(a.begin(), a.end());
  double min = 0;
  double max = l;
  double max1 = 0;
  for (long long i = 1; i < n; i++) {
    if ((a[i] - a[i - 1]) > max1) max1 = a[i] - a[i - 1];
  }
  min = a[0] - min;
  max = max - a[n - 1];
  max1 = max1 / 2;
  if (max1 > max && max1 > min)
    cout << fixed << setprecision(12) << max1;
  else if (max > min)
    cout << fixed << setprecision(12) << max;
  else
    cout << fixed << setprecision(12) << min;
  return 0;
}
