import itertools
N = int(input())
cnt = 0
T =  list(itertools.product(['0', '3', '6', '9'], repeat=len(str(N))))
for i in range(len(T)):
    num = int(''.join(T[i]))
    if num>10 and num<=N:
        cnt += 1

for i in range(10,min(100,N+1)):
    a,b = i//10 ,i%10
    if((a+b)%3==0 and a%3 != 0):
        cnt +=1

print(cnt)