#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

const int INF = (1 << 30) - 1;
const ll INF64 = ((ll)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

vector<bool> sieveOfEratosthenes(int n) {
	vector<bool> isPrime(n + 1, true);
	if (n >= 0) isPrime[0] = false;
	if (n >= 1) isPrime[1] = false;

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

	return isPrime;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	const int N_MAX = 20000;

	int n;
	cin >> n;

	vector<bool> isPrime = sieveOfEratosthenes(N_MAX + 1);
	vector<int> prime;
	for (int i = 2; i < isPrime.size(); i++) {
		if (isPrime[i]) {
			prime.emplace_back(i);
		}
	}

	vector<int> dp(N_MAX, -1);
	dp[0] = 0;
	for (auto u : prime) {
		for (int i = n; i >= 0; i--) {
			if (u + i > n || dp[i] == -1) {
				continue;
			}
			dp[u + i] = max(dp[u + i], dp[i] + 1);
		}
	}

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