import java.util.*;
import java.math.*;
public class Main {
    static final int MOD = 1_000_000_007; // 10^9+7
    //static final int MAX = 2_147_483_646; // intの最大値
    static final int INF = 1_000_000_000; // 10^9
    static final int MAX = 10_000_000;
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        Arrays.sort(ary);
        System.out.println(ary[n/2]-ary[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