from itertools import chain
inf = 10**18


def prime_set(N):
    """
    Nまでの素数のsetを返す
    """
    if N < 4:
        return ({}, {}, {2}, {2, 3})[N]
    Nsq = int(N ** 0.5 + 0.5) + 1
    primes = {2, 3} | set(chain(range(5, N + 1, 6), range(7, N + 1, 6)))
    for i in range(5, Nsq, 2):
        if i in primes:
            primes -= set(range(i * i, N + 1, i * 2))
    return primes


N = int(input())
prime = sorted(prime_set(N))

dp = [-inf] * (N + 1)
dp[0] = 0
for p in prime:
    for i in reversed(range(p, N + 1)):
        dp[i] = max(dp[i], dp[i - p] + 1)

if dp[N] < 0:
    print(-1)
else:
    print(dp[N])