import sys
sys.setrecursionlimit(100000000)
input = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = 10 ** 15

def main():
    A,B = map(int,input().split())
    a = A%3
    b = B%3
    ans = 0
    for i in range(A,B + 1):
        if (i%3 + a + b)%3 == 0:
            ans += 1
    print(ans)

if __name__ == '__main__':
    main()