source_code: 
  /**
   * Write a description of class VK2A here.
   * 
   * @author (your name) 
   * @version (a version number or a date)
   */
  import java.util.*;
  public class VK2A
  {
      public static void main(String args[])
      {
          Scanner S = new Scanner(System.in);
          int n = S.nextInt();
          int a = S.nextInt();
          int b = S.nextInt();
          int[] A = new int[n];
          for(int i = 0; i < n; i++)
              A[i] = S.nextInt();
          for(int i = 0; i < n; i++)
              for(int j = 0; j < n - i - 1; j++)
              {
                  if(A[j] < A[j + 1])
                  {
                      int temp = A[j];
                      A[j] = A[j + 1];
                      A[j + 1] = temp;
                  }
              }
          
              System.out.println(A[a - 1] - A[a]);
          }
   
  }
  