import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int A = scan.nextInt();
		int B = scan.nextInt();
		scan.close();
		int sum = A + B;
		int cnt = 0;
		for(int i = A; i <= B; i++) {
			int k = sum + i;
			if(k % 3 == 0) {
				cnt ++;
			}
		}
		System.out.println(cnt);
	}
}