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

#define pb         push_back

typedef long long ll;
const ll INF = 1000000000000000000ll;
const ll MOD = 1000000007ll;
const double EPS = 1e-8;

#define N 30000
bool prime[N];
vector<int> p;
int dp[20001];

void Eratos(int n){
	for(int i=0; i<n; i++){
		prime[i] = true;
	}
	prime[0] = prime[1] = false;

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

	p.pb(0);
	for(int i=0; i<n; i++){
		if(prime[i]){
			p.pb(i);
		}
	}
}

int main(void) {
	//ios_base::sync_with_stdio(false);
	//cin.tie(0);
	int n;
	cin >> n;

	Eratos(n+1);

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

	for(int i=1; i<p.size(); i++){
		for(int j=n; j>=0; j--){
			if(j + p[i] <= n && dp[j] != -1){
				dp[j + p[i]] = max(dp[j + p[i]], dp[j] + 1);
			}
		}
	}

	cout << dp[n] << endl;


	
	return 0;
}