import java.util.Arrays;
import java.util.Scanner;
public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int toi = scan.nextInt();
		int[] nanido = new int[toi];
		int re = 0;

		for(int i=0;i<toi;i++) {
			nanido[i] = scan.nextInt();
		}

		Arrays.sort(nanido);


			if(nanido[(toi/2)-1] == nanido[toi/2]) {
				re = 0;
			}else {
				re = nanido[toi/2] - nanido[(toi/2)-1];
			}

				System.out.println(re);
		scan.close();

	}

}

/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