import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
import itertools
if n<100:
	ans=0
	for i in range(10,n+1):
		i1,i2=str(i)[0],str(i)[1]
		if (int(i1)+int(i2))%3==0:
			ans+=1
	print(ans)
else:
	ans=0
	for i in range(10,100):
		i1,i2=str(i)[0],str(i)[1]
		if (int(i1)+int(i2))%3==0:
			ans+=1
	S=[0,3,6,9]
	for p in itertools.product(range(4),repeat=9):
		ct=0
		for i in range(9):
			ct+=S[p[i]]*10**i
		if 100<=ct<=n:
			ans+=1
	print(ans)