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

public class Main {
	public static void main(String arg[]) {

		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);

		System.out.print(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