def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

def max_prime_sum(N):
    primes = [i for i in range(1, N) if is_prime(i)]
    dp = [-1] * (N + 1)
    dp[0] = 0
    for prime in primes:
        for i in range(N - prime, -1, -1):
            if dp[i] != -1:
                dp[i + prime] = max(dp[i + prime], dp[i] + 1)
    return dp[N]

N = int(input())
print(max_prime_sum(N))