#include <iostream>
#include <algorithm>
#include <vector>
#include <utility>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
const int INF = (int)1e9 + 1;

bool is_prime[20010];
int dp[20010];

void eratos(int m) {
	for (int i = 0; i <= m; i++) {
		is_prime[i] = true;
	}
	is_prime[0] = is_prime[1] = false;

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

int main() {
	int n;
	cin >> n;
	for (int i = 0; i <= n; i++) {
		dp[i] = -1;
	}

	eratos(n);
	vector<int> prime;

	for (int i = 2; i < 20001; i++) {
		if (is_prime[i]) {
			prime.push_back(i);
		}
	}
	dp[0] = 0;

	for (auto u : prime) {
		for (int j = n; j >= 0; j--) {
			if (u + j <= n && dp[j] != -1) {
				dp[u + j] = max(dp[u + j], dp[j] + 1);
			}
		}
	}
	cout << dp[n] << endl;
	return 0;
}