#include<bits/stdc++.h>
#define MOD 1000000007
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3f
#define EPS (1e-10)
#define rep(i,n)for(int i=0;i<n;i++)
#define sqrt(s)sqrt(max(0.0,s))
using namespace std;
typedef long long ll;
typedef pair<int, int>P;

int dp[20001];
bool is_prime[20001];
int prime[2000];
int main() {
	memset(is_prime, 1, sizeof(is_prime));
	memset(dp, -1, sizeof(dp));
	is_prime[0] = is_prime[1] = false;
	int p = 0;
	int n; scanf("%d", &n);
	for (int i = 2; i <= n; i++) {
		if (is_prime[i]) {
			prime[p++] = i;
			for (int j = i * 2; j <= n; j += i)is_prime[j] = false;
		}
	}
	dp[0] = 0;
	rep(i, p) {
		for (int j = n - prime[i]; j >= 0; j--) {
			if (~dp[j])dp[j + prime[i]] = max(dp[j + prime[i]], dp[j] + 1);
		}
	}
	printf("%d\n", dp[n]);
}