#define _CRT_SECURE_NO_WARNINGS
#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<tuple>
#include<unordered_set>
#include<unordered_map>
#include<random>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())



//エラトステネスの篩 O(n loglog n)
#define MAX_N 20000
int prime[MAX_N];//i番目の素数
bool is_prime[MAX_N + 1];
int sieve(int n) {
	int p = 0;
	memset(is_prime, true, sizeof(is_prime));
	is_prime[0] = is_prime[1] = false;
	for (int i = 2; i <= n; i++) {
		if (is_prime[i]) {
			prime[p++] = i;
			for (int j = 2 * i; j <= n; j += i)is_prime[j] = false;
		}
	}
	return p;
}


int dp[20001];

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	int n;
	cin >> n;
	int np = sieve(n);
	fill_n(dp, n + 1, -INF);
	dp[0] = 0;
	rep(j, np) {
		for (int i = n - 1; i >= 0;i--) {
			if (i + prime[j] <= n)
				dp[i + prime[j]] = max(dp[i + prime[j]], dp[i] + 1);
		}
	}
	cout << (dp[n] < 0 ? -1 : dp[n]) << endl;

	return 0;
}