# https://yukicoder.me/problems/931
import math
N = int(input())


is_prime = [True for _ in range(N + 1)]
is_prime[0] = is_prime[1] = False
prime_list = []
for i in range(2, N + 1):
    if is_prime[i]:
        prime_list.append(i)
        for j in range(i * i, N + 1, i):
            is_prime[j] = False

dp = [-1 for _ in range(N + 1)]
dp[0] = 0
for i in prime_list:
    for j in range(N, i - 1, -1):
        if dp[j - i] != -1:
            dp[j] = max(dp[j - i] + 1, dp[j])

print(dp[N])
# print(dp)