#include <iostream>
#include <algorithm>
using namespace std;
int n, dp[20009]; bool prime[20009];
int main() {
	cin >> n;
	fill(prime + 2, prime + n + 1, true);
	fill(dp + 1, dp + n + 1, -999999999);
	for (int i = 2; i <= n; i++) {
		if (!prime[i]) continue;
		for (int j = i * i; j <= n; j += i) prime[j] = false;
		for (int j = n; j >= i; j--) dp[j] = max(dp[j], dp[j - i] + 1);
	}
	printf("%d\n", dp[n] >= 0 ? dp[n] : -1);
	return 0;
}