package main

import (
	"fmt"
	"math"
)

func main() {
	var a, b int
	_, _ = fmt.Scan(&a, &b)

	y := (6 - (a+b)%3 - a%3) % 3
	fmt.Println(int(math.Ceil(float64(b-a+1-y) / 3)))
}