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



int main() {
	int n;
	cin >> n;

	int dp[20001] = {};
	bool p[20001] = { true };
	int ma[20001] = {};
	p[0] = false;
	p[1] = false;
	for (int i = 0;i <= 20000;i++) {
		p[i] = true;
	}
	for (int i = 2;i <= 20000;i++) {
		if (p[i]) {
			dp[i] = 1;
			ma[i] = i;
			int j = 2;
			while (i*j <= 20000) {
				p[i*j] = false;
				j++;
			}
		}
	}

	for (int i = 2;i <= n;i++) {
		if (dp[i] == 0) {
			continue;
		}
		for (int j = ma[i]+1;i+j <= n;j++) {
			if (p[j]) {
				if (dp[i + j] < dp[i] + 1) {
					dp[i + j] = dp[i] + 1;
					ma[i + j] = j;
				}
				else if (dp[i + j] == dp[i] + 1) {
					ma[i + j] = min(ma[i + j], j);
				}
			}
		}
	}

	cout << ((dp[n] == 0) ? -1 : dp[n]) << endl;


	return 0;
}