import static java.lang.System.*;
import java.util.*;

public class Main {
	static Scanner sc = new Scanner(System.in);
	public static void main(String[] args) {
		int a = sc.nextInt(), b = sc.nextInt();
		int num = 0;
		for (int i=a; i<=b; i++) {
			if ((a+b+i)%3==0) num++;
		}
		out.println(num);
	}
}