#include <stdio.h>

int main(void) {
	double avg;
	int a, b, i, cnt = 0;
	
	scanf("%d %d", &a, &b);
	for(i = a ; i <= b ; i++){
		avg = (a+b+i)/3.0;
		if(avg == (int)avg){
			cnt++;
		}
	}
	printf("%d\n", cnt);
	return 0;
}