#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
using namespace std;
int N;
vector<int> dp;
vector<int> primes;
int idx = 0;
bool is_prime(int num)
{
	if (num < 2) return false;
	else if (num == 2) return true;
	else if (num % 2 == 0) return false; // 偶数はあらかじめ除く
	double sqrtNum = sqrt(num);
	for (int i = 3; i <= sqrtNum; i += 2)
	{
		if (num % i == 0)
		{
			return false;
		}
	}
	return true;
}
void set_prime() {
	for (int i = 0; i <= N; ++i) {
		if (is_prime(i)) {
			primes.push_back(i);
		}
	}
}
int main(void) 
{
	cin >> N;
	set_prime();
	dp.resize(N + 1, -1);
	dp[0] = 0;
	for (size_t p_idx = 0U; p_idx < primes.size(); ++p_idx) {
		int p = primes[p_idx];
		for (int n = N; n >= 0; --n) {
			if (n + p < N + 1 && dp[n] != -1) {
				dp[n + p] = max(dp[n + p], dp[n] + 1);
			}
		}
	}
	cout << dp[N] << endl;
	return 0;
}