import logging
import sys
from inspect import currentframe

sys.setrecursionlimit(10 ** 6)
input = sys.stdin.readline

logging.basicConfig(level=logging.DEBUG)


def sieve_eratosthenes(n):
    is_prime = [True] * (n + 1)
    is_prime[0] = is_prime[1] = False
    for i in range(2, n + 1):
        for j in range(2 * i, n + 1, i):
            is_prime[j] = False
    return is_prime


def dbg(*args):
    id2names = {id(v): k for k, v in currentframe().f_back.f_locals.items()}
    logging.debug(
        ", ".join(id2names.get(id(arg), "???") + " = " + repr(arg) for arg in args)
    )


def main():

    # 素数iを足す遷移を後ろから後ろから行う
    n = int(input())
    table = sieve_eratosthenes(n)
    dp = [-1] * (n + 1)
    # for i, fl in enumerate(table):
    #     if fl:
    #         dp[i] = 1
    dp[0] = 0
    for i, fl in enumerate(table):
        if fl:
            # for j in range(n, i, -1):
            for j in range(n, -1, -1):
                if dp[j] != -1 and j + i <= n:
                    dp[i + j] = max(dp[i + j], dp[j] + 1)
    # ans = max(dp)
    dbg(table)
    dbg(dp)
    ans = dp[n]
    print(ans)


if __name__ == "__main__":
    main()