import math

def prime_numbers(x):
    if x < 2:
        return []

    prime_numbers = [i for i in range(x)]
    prime_numbers[1] = 0

    for prime_number in prime_numbers:
        if prime_number > math.sqrt(x):
            break

        if prime_number == 0:
            continue

        for composite_number in range(2 * prime_number, x, prime_number):
            prime_numbers[composite_number] = 0

    return [prime_number for prime_number in prime_numbers if prime_number != 0]

n = int(input())
p = prime_numbers(n + 1)
dp = [-1] * (n + 1)
dp[0] = 0
for i in p:
    for j in range(n + 1)[::-1]:
        if i + j > n: continue
        if dp[j] != -1:
            dp[i + j] = max(dp[i + j], dp[j] + 1)
print(dp[n])