N = int(input())
memo = {}

def get_primes(n):
    numbers = set(range(n, 1, -1))
    primes = []
    while numbers:
        p = numbers.pop()
        primes.append(p)
        numbers.difference_update(set(range(p*2, n+1, p)))
    return primes

P = get_primes(N)

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

for p in P:
    for j in range(N, -1, -1):
        if p + j <= N and dp[j] != -1:
            dp[j + p] = max(dp[j + p], dp[j] + 1)

print(dp[N])