from collections import deque

n = int(input())

if n < 100:
    ans = 0
    for i in range(10,n+1):
        if i%3 == 0:
            if (int(str(i)[0])+int(str(i)[1]))%3 == 0:
                ans += 1
    print(ans)
    exit()
else:
    ans = 30
    q = deque([])
    for i in range(10,100):
        if i%3 == 0:
            if int(str(i)[0])%3 == 0 and int(str(i)[1])%3 == 0:
                q.append(str(i))
    while q:
        now = q.popleft()
        if int(now) > n:
            continue
        if int(now) >= 100:
            ans += 1
        q.append(now+"3")
        q.append(now+"6")
        q.append(now+"9")
        q.append(now+"0")
        
    print(ans)