# https://yukicoder.me/problems/no/1185
from decimal import Decimal
from itertools import combinations

N = Decimal(input().strip())
count = 0
i = 12
while i <= N:
    if i % 3 != 0:
        i += 1
        continue

    l = list(combinations(str(i), 2))

    tf = True
    for j in l:
        if sum(list(map(int, j))) % 3 != 0:
            tf = False

    if tf:
        count += 1

    i += 1

print(count)