import java.util.*;

public class Main {
	
	public static void main(String[] args)  {
		Scanner scan = new Scanner(System.in);
		int n=Integer.parseInt(scan.next());
		int[] d=new int[n];
		for (int i=0;i<n;++i) {
			d[i]=Integer.parseInt(scan.next());
		}
		Arrays.parallelSort(d);
		if (d[n/2]==d[n/2-1]) {
			System.out.print(0);
		}else {
			System.out.print(d[n/2]-d[n/2-1]);
		}
		
}
}
//end
/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