#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>
#include<limits>
#include<iterator>

#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define rep(i,n) for(int i=0; i<n; i++)
#define FOR(i,a,n) for(int i=a; i<n; i++)

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ll, char> plc;
typedef pair<string, string> pss;

int arr[100010];
int dp[20010];
vector<int> v;
int n;

void Eratosthenes() {
	rep(i, 20001)arr[i] = 1;

	FOR(i, 2, sqrt(20001)) {
		if (arr[i]) {
			for (int j = 0; i*(j + 2) < 20001; j++)
				arr[i*(j + 2)] = 0;
		}
	}
}


int main()
{
	cin >> n;
	Eratosthenes();
	
	rep(i, n + 1)dp[i] = -1;

	for (int i = 2; i < 20001; i++) {
		if (arr[i])v.push_back(i);
	}
	
	dp[0] = 0;

	for (auto u : v) {
		for (int j = n; j >= 0; j--) {
			if (u + j <= n && dp[j] != -1) {
				dp[u + j] = max(dp[u+j],dp[j]+1);
			}
		}
	}
	cout << dp[n] << endl;
	return 0;
}