import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int num = Integer.parseInt(in.nextLine());
    List<Integer> dif = new ArrayList<>();
    while(in.hasNext()){
      dif.add(Integer.parseInt(in.next()));
    }
    Collections.sort(dif);
    int ans = dif.get(num / 2) - dif.get(num / 2 - 1);
    System.out.println(ans);
  }
}
      
/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