#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include<math.h>
#define rep(i,a) for(int i=0;i<a;i++)
#define nrep(i,a,b) for(int i=a;i<b;i++)
#define mrep(i,a) for(int i=a;i>=0;i--)
#define ll long long
#define INF 11451419191810
using namespace std;

int main(){

	ll n;  cin >> n;
	vector<bool> prime(n + 1,true);
	prime[0] = false;
	prime[1] = false;
	ll index = 2;
	while (index*index <= n){
		if (prime[index]){
			ll j = index + index;
			while (j <= n){
				prime[j] = false;
				j += index;
			}
		}index++;
	}ll count = 0;
	vector<ll> p;
	rep(i, n + 1) if (prime[i]) p.push_back(i);

	vector<ll> dp(n + 1, -1);
	dp[0] = 0;
	for (ll i : p){
		mrep(j, n){
			if (i + j <= n && dp[j] != -1){
				dp[i + j] = max(dp[i + j], dp[j] + 1);
			}
		}
	}cout << dp[n] << endl;

	return 0;
}