#include<iostream>
#include<vector>
#include<algorithm>
#include<math.h>
using namespace std;
int main() {

	int N;
	cin >> N;

	vector<int> arr(N), s;
	for (int i = 0; i < N; i++) {
		arr[i] = 1;
	}
	for (int i = 2; i < sqrt(N); i++) {
		if (arr[i]) {
			for (int j = 0; i * (j + 2) < N; j++) {
				arr[i *(j + 2)] = 0;
			}
		}
	}
	for (int i = 2; i < N; i++) {
		if (arr[i]) {
			s.push_back(i);
		}
	}
	
	int dp[20001];
	for (int i = 0; i < N + 1; i++)dp[i] = -1;
	dp[0] = 0;

	for (auto i : s) {
		for (int j = N; j >= 0; j++) {
			if (dp[j] != -1 && i + j <= N) {
				dp[i + j] = max(dp[i + j], dp[j] + 1);
			}
		}
	}
	cout << dp[N] << endl;

	return 0;
}