import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	A, B = getlist()
	ans = 0
	for i in range(A, B + 1):
		if (A + B + i) % 3 == 0:
			ans += 1

	print(ans)




if __name__ == '__main__':
	main()