licznik = 0
while True:
try:
x = int(input())
if x == 0:
break
if x % 3 == 0:
licznik += 1
except EOFError:
break
print(licznik)
bGljem5payA9IDAKd2hpbGUgVHJ1ZToKICB0cnk6CiAgICB4ID0gaW50KGlucHV0KCkpCiAgICBpZiB4ID09IDA6CiAgICAgICAgYnJlYWsKICAgIGlmIHggJSAzID09IDA6CiAgICAgICAgbGljem5payArPSAxCiAgZXhjZXB0IEVPRkVycm9yOgogICAgICBicmVhawpwcmludChsaWN6bmlrKQogICA=