import java.util.*;
import java.awt.*;

class Main {

    private static Scanner sc = new Scanner(System.in);

    //ソート Arrays.sort(配列名);
    //逆順ソート Arrays.sort(配列名,  Collections.reverseOrder());


    public static void main(String[] args) {
        int n = Integer.parseInt(sc.next());
        int[] d = new int[n];
        int ans=0;

        for(int i = 0;i < n; i++){
            d[i] = Integer.parseInt(sc.next());
        }
        Arrays.sort(d);
        ans = d[n/2]-d[n/2-1];

        System.out.println(ans);
    }
}

/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