#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>

using namespace std;

vector<int> get_primes(int n) {
	vector<bool> is_prime(n + 1, true);
	is_prime[0] = is_prime[1] = false;

	for (int i = 2; i * i <= n; i++) {
		if (is_prime[i]) {
			for (int j = i * 2; j <= n; j += i) {
				is_prime[j] = false;
			}
		}
	}

	vector<int> primes;
	for (int i = 0; i <= n; i++) {
		if (is_prime[i]) {
			primes.emplace_back(i);
		}
	}

	return primes;
}

int main() {
	int n;
	cin >> n;

	auto primes = get_primes(n);

	vector<int> dp(n + 1, -1);
	dp[0] = 0;

	for (auto prime : primes) {
		for (int i = n; i >= 0; i--) {
			if (dp[i] == -1) {
				continue;
			}

			int x = i + prime;
			if (x <= n) {
				dp[x] = max(dp[x], dp[i] + 1);
			}
		}
	}

	cout << dp[n] << endl;
	return 0;
}