#include "bits/stdc++.h"

using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;
bool is_prime[20001];
int dp[20001];
int main() {
	int N;
	cin >> N;
	memset(is_prime, -1, sizeof(is_prime));
	for (int i = 2; i <= N; i++) {
		if (!is_prime[i]) continue;
		for (int j = i * 2; j <= N; j += i) is_prime[j] = 0;
	}
	vector<int> prime;
	for (int i = 2; i <= N; i++) if (is_prime[i]) prime.push_back(i);
	memset(dp, -1, sizeof(dp));
	dp[0] = 0;
	for (int i = 0; i < prime.size(); i++) {
		for (int j = N; j >= prime[i]; j--) {
			if (dp[j - prime[i]] != -1) dp[j] = max(dp[j], dp[j - prime[i]] + 1);
		}
	}
	cout << dp[N] << endl;
}