#include <bits/stdc++.h>
using namespace std;
vector<long double> vi;
long double n, m, a, s, r, ma;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; ++i) {
    cin >> a;
    vi.push_back(a);
    s += a;
  }
  sort(vi.begin(), vi.end());
  for (int i = 1; i < n; ++i) {
    ma = max(ma, vi[i] - vi[i - 1]);
  }
  r = ma / 2;
  cout << fixed << setprecision(10) << max(r, max(vi[0], m - vi[n - 1]));
  return 0;
}
