## https://yukicoder.me/problems/no/707

MAX_INT = 10 ** 18

def main():
    N = int(input())

    primes = []
    is_primes = [True for _ in range(N + 1)]
    is_primes[1] = False
    for p in range(2, N + 1):
        if not is_primes[p]:
            continue
        x = 2 * p
        primes.append(p)
        while x <= N :
            is_primes[x] = False
            x += p

    dp = [-1] * (N + 1)
    dp[0] = 0

    for p in primes:
        for i in reversed(range(N + 1)):
            if dp[i] == -1:
                continue

            if i + p <= N:
                dp[i + p] = max(dp[i] + 1, dp[i + p])

    if dp[-1] == -1:
        print(-1)
    else:
        print(dp[-1])








if __name__ == "__main__":
    main()