import java.util.*;
public class Main{
	public static void main(String arg[]){
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		int a[]=new int[n];
		for(int i=0;i<n;i++)
			a[i]=sc.nextInt();
		Arrays.sort(a);
		int m=a.length/2;
		if(a[m]==a[m-1])
			System.out.println("0");
		else{
			if(a[m-1]!=a[m])
				System.out.println(a[m]-a[m-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