import sys
def input(): return sys.stdin.readline().strip()
def mapint(): return map(int, input().split())
sys.setrecursionlimit(10**9)

N = int(input())

def dfs(idx, string):
    if idx==length:
        ret.append(string)
        return
    for nx in ['0', '3', '6', '9']:
        dfs(idx+1, string+nx)

if N<=100:
    print(N//3-3)
else:
    ans = 100//3-3
    length = len(str(N))
    ret = []
    dfs(0, '')
    for s in ret:
        n = int(s)
        if 100<=n<=N:
            ans += 1
    print(ans)