A, B = list(map(int, input().split()))
res = 0 if (A + B) % 3 == 0 else 3 - (A + B) % 3
start = A if res == A % 3 else A + abs(res - (A % 3))
end = B if res == B % 3 else B - abs(3 + B % 3 - res if B > B % 3 else 0)
print(0 if end - start < 3 else (end - start)//3 + 1)