from itertools import *

N = int(input())
ans = 0
for i in range(10, min(100, N + 1)):
    s = str(i)
    a, b = int(s[0]), int(s[1])
    if (a + b) % 3 == 0:
        ans += 1
        
for tup in product(["3", "6", "9", "0"], repeat=10):
    n = int("".join(tup))
    if 100 < n <= N:
        ans += 1
print(ans)