import java.util.*;

public class Main{

    public static void main(String args[]){

        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();
        }


        Arrays.sort(d);

        if (n%2!=0){
            System.out.println(0);
        }else if(d[(n/2)-1]==d[n/2]){
            System.out.println(0);
        }else{
            System.out.println(d[n/2]-d[(n/2)-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