N = int(input())

import sys
sys.setrecursionlimit(10**7)

def dfs(n):
    if 100 <= n <= N:
        nums.append(n)
    for i in [0, 3, 6, 9]:
        if n * 10 + i <= N:
            dfs(n * 10 + i)

nums = []
dfs(3)
dfs(6)
dfs(9)
#print(nums)
ans = 0
if N <= 100:
    ans = N // 3 - 10 // 3
else:
    ans = 100 // 3 - 10 // 3
    ans += len(nums) 
print(ans)