import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		int[] array = new int[n];
        int count = 0;
        
        //初期化
        for(int i = 0; i < n; i++){
		    array[i] = sc.nextInt();
		}
		
		Arrays.sort(array);
		
		int m = n/2;
		System.out.println(array[m]-array[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