import java.util.*;

public class Main{
    public static void main(String[] args){
    //入力
        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();
        }
    //処理
        Arrays.sort(D);
        System.out.println(D[N/2]-D[N/2-1]);

        sc.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