import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();
        int b = in.nextInt();

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

        System.out.println(count);
    }
}