import java.util.Scanner;

public class Main {


    public static void main(String[] args) {

    	Main main=new Main();

    	main.run();

    }

    void run() {
    	Scanner sc=new Scanner(System.in);

    	int A=sc.nextInt();
    	int B=sc.nextInt();

    	int counter=0;

    	for(int i=A;i<=B;i++) {

    		if(i%3==0) {
    			counter++;
    		}

    	}

    	System.out.println(counter);

    }



}