from collections import defaultdict


# nより小さい素数のリストを生成
def make_prime_list(n):
    num = [True] * n
    num[0] = num[1] = False
    for i in range(2, int(n ** 0.5) + 1):
        if num[i]:
            for j in range(i ** 2, n, i):
                num[j] = False

    return [i for i in range(2, n) if num[i]]


def main():
    n = int(input())
    prime_list = make_prime_list(n + 1)
    dp = [-1] * (n + 1)
    dp[0] = 0
    for prime in prime_list:
        for i in range(len(dp) - 1, -1, -1):
            if dp[i] != -1 and i + prime < len(dp):
                dp[i + prime] = max(dp[i + prime], dp[i] + 1)

    print(dp[n])


if __name__ == '__main__':
    main()