Polycarp likes numbers that are divisible by 3.

He has a huge number $s$. Polycarp wants to cut from it the maximum number of numbers that are divisible by $3$. To do this, he makes an arbitrary number of vertical cuts between pairs of adjacent digits. As a result, after $m$ such cuts, there will be $m+1$ parts in total. Polycarp analyzes each of the obtained numbers and finds the number of those that are divisible by $3$.

For example, if the original number is $s=3121$, then Polycarp can cut it into three parts with two cuts: $3|1|21$. As a result, he will get two numbers that are divisible by $3$.

Polycarp can make an arbitrary number of vertical cuts, where each cut is made between a pair of adjacent digits. The resulting numbers cannot contain extra leading zeroes (that is, the number can begin with 0 if and only if this number is exactly one character '0'). For example, 007, 01 and 00099 are not valid numbers, but 90, 0 and 10001 are valid.

What is the maximum number of numbers divisible by $3$ that Polycarp can obtain?
The first line of the input contains a positive integer $s$. The number of digits of the number $s$ is between $1$ and $2\cdot10^5$, inclusive. The first (leftmost) digit is not equal to 0.
3121
2
6
1
1000000000000000000000000000000000
33
201920181
4
4
0
10
1
11
0
12
1
13
1
31
1
14139582796
6
1670000
5
604500
5
40041
2
10000170
5
import sys
import math
import bisect
import heapq
import itertools
from itertools import accumulate
from sys import stdin,stdout
from math import gcd,floor,sqrt,log, ceil,inf
from collections import defaultdict, Counter, deque
import heapq
from bisect import bisect_left,bisect_right, insort_left, insort_right
mod=1000000007
def get_ints(): return map(int, sys.stdin.readline().strip().split())
def get_list(): return list(map(int, sys.stdin.readline().strip().split()))
def get_string(): return sys.stdin.readline().strip()
def get_int(): return int(sys.stdin.readline().strip())
def get_list_strings(): return list(map(str, sys.stdin.readline().strip().split()))
 
def solve():
    number = list(map(int,list(input())))
    arr = [0] + list(accumulate(number))
    for i in range(len(arr)):
          arr[i] %= 3

    pre = [[inf,inf,inf] for i in range(len(arr)-1)]
    pre[-1][arr[-1]] = len(pre)-1

    for i in range(len(pre)-2,-1,-1):
          pre[i] = pre[i+1].copy()
          pre[i][arr[i+1]] = i
    leng = len(number)

    memo = {}
    def dp(n):
        if n > leng:return 0
        if n not in memo:
            cur = pre[n-1][arr[n-1]] + 2
            if cur == inf: memo[n] = dp(n+1)
            else: memo[n] = max(dp(cur)+1,dp(n+1))
        return memo[n]
    return dp(1)
         


 
    
 
 
 
 
 
if __name__ == "__main__":
        print(solve())