import java.util.Scanner;
import java.util.Arrays;


public class Main
{
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int N;
        long L;
        N = in.nextInt();
        L = in.nextLong();

        double a[] = new double[N];
        for (int i = 0; i < N; ++i) {
            a[i] = in.nextDouble();
        }
        Arrays.sort(a);

        double dist[] = new double[N + 1];
        dist[0] = a[0] - 0.000000000;
        for (int i = 1; i < N; ++i) {
            dist[i] = a[i] - a[i - 1];
        }
        dist[N] = L - a[N - 1];

        Arrays.sort(dist);
        System.out.println(dist[N] / 2);
    }

}