#include <stdio.h>


int main(){
	setvbuf(stdout,NULL,_IONBF,0);
	int i,a,b,count=0;
	scanf("%d%d",&a,&b);
	for(i=a;i<=b;i++){
		if((a+b+i)%3==0)count++;}
		printf("%d\n",count);
	}