def sieve(n):
    if n < 2:
        return []
    is_prime = [True] * (n + 1)
    is_prime[0] = is_prime[1] = False
    for i in range(2, int(n ** 0.5) + 1):
        if is_prime[i]:
            for j in range(i * i, n + 1, i):
                is_prime[j] = False
    primes = [i for i, val in enumerate(is_prime) if val]
    return primes

n = int(input())
primes = sieve(n)

if not primes:
    print(-1)
else:
    dp = [-1] * (n + 1)
    dp[0] = 0
    for p in primes:
        for j in range(n, p - 1, -1):
            if dp[j - p] != -1:
                dp[j] = max(dp[j], dp[j - p] + 1)
    print(dp[n] if dp[n] != -1 else -1)