#include<iostream>
#include<vector>
typedef long long ll;
typedef long double ld;
using namespace std;
ll prime(ll x) {
	ll i;
	if (x < 2)return 0;
	else if (x == 2) return 1;
	if (x % 2 == 0) return 0;
	for (i = 3; i*i <= x; i += 2) {
		if (x%i == 0) return 0;
	}
	return 1;
}
int main() {
	ll N;
	cin >> N;
	vector<ll>v;
	for (ll i = 2; i <= 20000; i++) {
		if (prime(i)) {
			v.push_back(i);
		}
	}
	ll dp[20010];
	for (ll i = 0; i <= 20000; i++) {
		dp[i] = -1;
	}
	dp[0] = 0;
	for (ll i = 0; i<v.size(); i++) {
		for (ll j = N; j >= 0; j--) {
          	if(dp[i]==-1) continue;
			if (v[i] + j <= N ) {
				dp[j + v[i]] = max(dp[j + v[i]], dp[j] + 1);
			}
		}

	}

	cout << dp[N] << endl;
}