import java.util.*;
 
public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
        int nam[] = new int[n];
      
      for(int i = 0 ;i < n ;i++){
       nam[i] =  in.nextInt();
      }
      Arrays.sort(nam);
     
      if(nam[(n/2)-1]==nam[n/2]){System.out.print(0);}
      else{System.out.print(nam[n/2]-nam[(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