#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, l, a[1005];
  cin >> n >> l;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  double ans = -1;
  if (a[0] > ans) {
    ans = a[0];
  }
  for (int i = 1; i < n; i++) {
    if ((double)(a[i] - a[i - 1]) / 2 > ans) {
      ans = (double)(a[i] - a[i - 1]) / 2;
    }
  }
  if ((double)(l - a[n - 1]) > ans) {
    ans = (double)l - a[n - 1];
  }
  cout << fixed << setprecision(9) << ans;
}
