import java.io.*;
import java.util.*;


public class Main_yukicoder682 {

	private static Scanner sc;
	private static Printer pr;

	private static void solve() {
		int a = sc.nextInt();
		int b = sc.nextInt();

		int cnt = 0;
		for (int i = a; i <= b; i++) {
			if ((a + i + b) % 3 == 0) {
				cnt++;
			}
		}

		pr.println(cnt);
	}

	// ---------------------------------------------------
	public static void main(String[] args) {
		sc = new Scanner(INPUT == null ? System.in : new ByteArrayInputStream(INPUT.getBytes()));
		pr = new Printer(System.out);

		solve();

//		pr.close();
		pr.flush();
//		sc.close();
	}

	static String INPUT = null;

	private static class Printer extends PrintWriter {
		Printer(OutputStream out) {
			super(out);
		}
	}
}