using namespace std;
#include<iostream>
#include<algorithm>
#include<cstring>
#include<vector>
#include<cmath>
int N;
int dp[20009];
vector<int> prime;
vector<bool>  isprime(20009);

int main() {
	cin >> N;
	for (int i = 2; i <= N; i++) {
		isprime[i] = 1;
	}
	for (int j = 2; j <= int(sqrt(N)); j++) {
		for (int k=2; j*k <= N; k++) {
			isprime[j * k] = 0;
		}
	}
	for (int i = 2; i <= N; i++) {
		if (isprime[i]) {
			prime.push_back(i);
		}
	}
	memset(dp, -1, sizeof(dp));
	dp[0] = 0;
	for (auto pr : prime) {
		for (int j = N; j >= 0; j--) {
			if (j + pr <= N and dp[j] != -1) {
				if (dp[j + pr] < dp[j] + 1) dp[j + pr] = dp[j] + 1;
			}
		}
	}
	cout << dp[N] << endl;
}