from sys import stdin, stdout, stderr

def solve():
    N = int(input())
    ps = make_primes(N + 1)

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

    for p in ps:
        for i in range(N, p - 1, -1):
            dp[i] = max(dp[i], dp[i - p] + 1)

    # print(dp)
    ans = dp[N]

    if ans > 0:
        print(ans)
    else:
        print(-1)


def make_primes(N):
    sieve = [True] * N
    sieve[0] = sieve[1] = False

    for p in range(2, N):
        if not sieve[p]:
            continue

        for m in range(p**2, N, p):
            sieve[m] = False

    return [i for i in range(N) if sieve[i]]

if __name__ == '__main__':
    solve()