#include <bits/stdc++.h>
using namespace std;
double n = 0.0;
int x, y, a[1000100], mx, mx2;
int main() {
  cin >> x >> y;
  for (int i = 0; i < x; i++) {
    cin >> a[i];
  }
  sort(a, a + x);
  for (int i = 0; i < x - 1; i++) {
    mx = max(mx, (a[i + 1] - a[i]));
  }
  mx = max(mx, (y - a[x - 1]) * 2);
  mx = max(mx, a[0] * 2);
  n = mx;
  cout << fixed << setprecision(9) << n / 2;
}
