source_code: import java.util.Scanner;
  
  public class Main{
      public static void main(String[] args){
          Scanner in = new Scanner(System.in);
          int n = in.nextInt();
          int a = in.nextInt();
          int b = in.nextInt();
          
          int[] h = new int[3000];
          
          for(int i = 0; i<n; i++)
              h[i] = in.nextInt();
          
          int l = 0, r = 1000000000, m = 0;
          int ansl = 0, ansr = 0;
          
          while(l<=r){
              m = (l+r)/2;
              
              int ca=0;
              
              for(int i = 0;i<n;i++)
                  if (h[i]>m) ca++;
              
              if (ca == a) ansl=m;
              if (ca <= a) r=m-1; else l=m+1;
          }
          l = 0; r = 1000000000;
          while(l<=r){
              m = (l+r)/2;
              
              int ca=0;
              
              for(int i = 0;i<n;i++)
                  if (h[i]>m) ca++;
              
              if (ca == a) ansr=m;
              if (ca < a) r=m-1; else l=m+1;
          }
          if (ansl == 0 || ansr==0) System.out.print(0); else
          System.out.print(ansr-ansl+1);
      }
  }