#!/usr/bin/env python3

from sys import setrecursionlimit, stdin
from typing import Iterable

INF: int = 2**62
MOD: int = 10**9 + 7

setrecursionlimit(10**6)


def inputs(type_=int):
    ins = input().split(' ')
    ins = [x for x in ins if x != '']

    if isinstance(type_, Iterable):
        return [t(x) for t, x in zip(type_, ins)]
    else:
        return list(map(type_, ins))


def input_(type_=int):
    a, = inputs(type_)
    return a


inputi = input_


def inputstr():
    return input_(str)


# b/a縺ｮ蛻・ｊ荳翫￡
def ceil(b, a):
    return (a + b - 1) // a


def answer(res) -> None:
    print(res)
    exit()


def compute():
    return

def prime_iter():
    """
    繧ｨ繝ｩ繝医せ繝・ロ繧ｹ縺ｮ遽ｩ
    險育ｮ鈴㍼縺ｯ O(n * sqrt(n) / log(n))
    """
    ps = []
    n = 2
    while True:
        for k in ps:
            if n % k == 0:
                break
            elif k * k > n:
                ps.append(n)
                yield n
                break
        else:
            ps.append(n)
            yield n

        n += 1

def main():
    n = inputi()

    # ps[i]: i逡ｪ逶ｮ縺ｫ蟆上＆縺・ｴ謨ｰ (ps[i] <= max(n//2, p-n//2))
    # pi = len(ps)
    # dp[i][k]: ps[i]繧剃ｽｿ縺｣縺ｦk繧剃ｽ懊ｋ譎ゅ・譛€螟ｧ縺ｮ蜥後・蝗樊焚
    #
    # dp[0][0] = 0
    # 蛻晄悄蛹・ dp = [[-1] * (n+1) for _ in range(ps)]
    # 譖ｴ譁ｰ:
    #     dp[i][k] = max(dp[i][k-1], dp[i-1][k-ps[i]] + 1)
    # 蜃ｺ蜉・ dp[-1][n]

    ps = []
    iter_ = prime_iter()
    while True:
        p = next(iter_)
        if p > n:
            break
        ps.append(p)

    ps = [0] + ps
    plen = len(ps)
    dp = [[-1] * (n+1) for _ in range(plen)]
    dp[0][0] = 0

    for i in range(1, plen):
        for k in range(n+1):
            dp[i][k] = dp[i-1][k]
            if k - ps[i] >= 0 and dp[i-1][k-ps[i]] >= 0:
                dp[i][k] = max(1 + dp[i-1][k-ps[i]], dp[i-1][k])

    # from pprint import pprint
    # pprint(dp)
    print(dp[-1][n])


if __name__ == '__main__':
    main()