import java.util.Scanner;

class no682{
	public static void main(String[] args) {
		Scanner stdIn=new Scanner(System.in);
		int a,b,i,s=0;
		a=stdIn.nextInt();
		b=stdIn.nextInt();
		for(i=a;i<=b;i++) if((a+b+i)%3==0) s++;
		System.out.print(s);
	}
}