c=0 #niepodzielne
b=0 #podzielne
a = int(input())
while a!=0:
if a % 3 == 0: b=b+1
else: c=c+1
a=int(input())
print(b)
Yz0wICNuaWVwb2R6aWVsbmUKYj0wICNwb2R6aWVsbmUKYSA9IGludChpbnB1dCgpKQp3aGlsZSBhIT0wOgoJaWYgYSAlIDMgPT0gMDogYj1iKzEKCWVsc2U6IGM9YysxCglhPWludChpbnB1dCgpKQpwcmludChiKQ==