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

class Main {

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

	int N = sc.nextInt();
	int d[] = new int[N];
	for (int i = 0; i < N; i++)
	    d[i] = sc.nextInt();

	Arrays.sort(d);
	if (d[(N / 2) - 1] == d[N / 2])
	    System.out.println(0);
	else
	    System.out.println(d[N / 2] - d[(N / 2) - 1]);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz