#include <stdio.h>

int main(void){
	int a, b, i, j;
	int s = 0;

	do {
		scanf("%d", &a);
		scanf("%d", &b);
	} while(a > b || b > 100 || a <= 0);

	for (i = a; i <= b; i++) {
		int sum;
		sum = a + b + i;

		if (sum % 3 == 0)
			s++;
	}
		printf("%d\n", s);

	return 0;
}