#include "bits/stdc++.h"
using namespace std;

bool P[20010] = {};
vector<int> prime;
int DP[20010] = {};

int main() {
	int N;
	cin >> N;
	for (int i = 2; i <= 20000; i++) P[i] = true;
	for (int i = 2; i * i <= 20000; i++) {
		if (P[i]) {
			for (int j = 2; i * j <= 20000; j++) {
				P[i * j] = false;
			}
		}
	}
	for (int i = 2; i <= 20000; i++) {
		if (P[i]) prime.push_back(i);
	}
	for (int i = 1; i <= 20000; i++) DP[i] = -1000000000;
	for (int X : prime) {
		for (int i = 20000 - X; i >= 0; i--) {
			DP[i + X] = max(DP[i + X], DP[i] + 1);
		}
	}
	if (DP[N] >= 0) cout << DP[N];
	else cout << -1;
}