import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class Main {

	void run() {
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		int ans = 0;
		for (int i = A; i <= B; ++i) {
			if ((i + A + B) % 3 == 0)
				++ans;
		}
		System.out.println(ans);
	}

	public static void main(String[] args) {
		new Main().run();
	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}