#include <bits/stdc++.h>
using namespace std;

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

int main(){
	int N;
	cin >> N;
	
	memset(is_prime, -1, sizeof(is_prime));
	vector<int> primes;
	for(int i = 2; i <= N; i++){
		if(!is_prime[i]) continue;
		primes.push_back(i);
		for(int j = i * 2; j <= N; j += i) is_prime[j] = false;
	}
	
	memset(dp, -1 ,sizeof(dp));
	dp[0]=0;
	for(auto p:primes){
		for(int i = N; i - p >= 0; i--){
			if(dp[i - p] != -1) dp[i] = max(dp[i], dp[i - p] + 1);
		}
	}
	
	cout << dp[N] << endl;
	return 0;
}