A, B = map(int,input().split())
C = A + B
L = [i for i in range(A, B+1)]
cnt = 0
if C % 3 == 0:
    for i in L:
        if i % 3 == 0:
            cnt += 1
elif C % 3 == 1:
    for i in L:
        if i % 3 == 2:
            cnt += 1 
elif C % 3 == 2:
    for i in L:
        if i % 3 == 1:
            cnt += 1
print(cnt)