#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <iomanip>
#include <stdio.h>
#include <numeric>
#include <math.h>
#include <algorithm>
#include <functional>
#include <string>
#include <array>
#include <vector>
#include <list>
#include <stack>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <deque>
#include <queue>
#include <complex>
#include <bitset>
#define full(c) c.begin(), c.end()
#define vector2d(name,type,h,w,init) vector<vector<type>> name(h,vector<type>(w,init)) 
const int PRIME = 1000000007;
const int INT_INF = 2147483647;
const long long int LL_INF = 9223372036854775807;
const double PI = acos(-1);
const double EPS = 0.0001;
typedef unsigned long long int ull;
typedef long long int ll;
using namespace std;

int main() {
	//cin.tie(0);
	//ios::sync_with_stdio(false);
	int n;
	cin >> n;
	vector<int> prime;
	vector<int> cnt(n + 1, -1);
	{
		const int PMAX = 40000;
		vector<bool> flag(PMAX + 1, true);
		flag[0] = false;
		flag[1] = false;
		for (int k = 2; k*k <= PMAX; k++) {
			for (int i = 2; k*i <= PMAX; i++) {
				flag[k*i] = false;
			}
		}
		for (int i = 0; i <= PMAX; i++) {
			if (flag[i]) prime.push_back(i);
		}
	}
	cnt[0] = 0;
	for (int i = 0; i < prime.size(); i++) {
		for (int k = n; k >= prime[i]; k--) {
			if (cnt[k - prime[i]] != -1) {
				cnt[k] = max(cnt[k], cnt[k - prime[i]] + 1);
			}
		}
	}
	cout << cnt[n] << endl;
	return 0;
}