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

typedef pair<int, int> P;
typedef unsigned long long ll;

const int inf = 999999999;
const int mod = 1000000007;

vector<int> eratosthenes(int n){
	bool arr[n];
	for(int i = 0; i <= n; i++){
		arr[i] = true;
	}
	arr[0] = false; arr[1] = false;
	for(int i = 2; i * i <= n; i++){
		if(arr[i]){
			for(int j = i * 2; j <= n; j += i){
				arr[j] = false;
			}
		}
	}
	vector<int> primes;
	for(int i = 0; i <= n; i++){
		if(arr[i]) primes.push_back(i);
	}
	return primes;
}

int main(){
	int n; cin >> n;
	vector<int> primes = eratosthenes(n);
	vector<int> dp(n + 1, -1);
	dp[0] = 0;
	for(int k = 0; k < primes.size(); k++){
		int p = primes[k];
		for(int i = n; i >= 0; i--){
			if(i + p < n + 1 && dp[i] != -1){
				dp[i + p] = max(dp[i + p], dp[i] + 1);
			}
		}
	}
	cout << dp[n] << endl;
	return 0;
}