N = int(input())
INF = 1 << 30

def list_primes(limit):
    primes = []
    is_prime = [True] * (limit + 1)
    is_prime[0] = False
    is_prime[1] = False

    for p in range (0, limit + 1):
        if not is_prime[p]:
            continue
        primes.append(p)
        for i in range(p*p, limit + 1, p):
            is_prime[i] = False

    return primes

primes = list_primes(N)

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

for p in primes:
    for i in range(N+1)[::-1]:
        if i - p < 0:
            break
        dp[i] = max(dp[i], dp[i-p] + 1)

print(dp[-1] if dp[-1] > 0 else -1)