import java.util.*;

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