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

int main() {
	vector<int> ps;
	ps.emplace_back(2);
	for (int i = 3; i <= 20000; i += 2) {
		for (int p : ps) {
			if (i % p == 0) {
				goto next;
			}
		}
		ps.emplace_back(i);
		next:;
	}
	int n;
	cin >> n;
	int dp[n + 1];
	fill(dp, dp + n + 1, -1);
	dp[0] = 0;
	for (auto p : ps) {
		for (int i = n; i; i--) {
			if (i - p < 0) {
				break;
			}
			if (0 <= dp[i - p]){
				dp[i] = max(dp[i], dp[i - p] + 1);
			}
		}
	}
	cout << dp[n] << endl;
	return 0;
}