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

public class Main {
	public static void main(String[]args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] dif = new int[n];
		int max = 0;
		for(int i = 0; i < n; i++){
			dif[i] = sc.nextInt();
		}
		Arrays.sort(dif);
		
		int res= dif[dif.length/2] - dif[dif.length/2 - 1];
		System.out.println(res);
	}
}
/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