import java.util.*; import java.util.Arrays; public class Main { public static void main(String[] args){ Scanner sc = new Scanner(System.in); int a1 = 21;//sc.nextDouble(); int a2 = 9;//sc.nextInt(); int a3 = 3;//sc.nextInt(); System.out.println((a3*(a3-a1)+a2*(a2-a3))/(a2-a1)); } }