import java.util.*;
import java.util.stream.*;

class Main{
	static Scanner s=new Scanner(System.in);
	static int gInt(){
		return Integer.parseInt(s.next());
	}
	public static void main(String[] A){
		int a=gInt(),b=gInt();
		System.out.println(IntStream.range(a,b+1).filter(i->(a+b+i)%3==0).count());
	}
}