#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;

const int MAX=20001;
const int INF=1e9;
vector<int> prime;
bool isprime[MAX];
 
void sieve(){
	for(int i=3; i<MAX; i+=2){
		isprime[i]=1;
	}
	isprime[2]=1;
	prime.push_back(2);
	for(int i=3; i<MAX; i++){
		if(isprime[i]){
			prime.push_back(i);
			for(int j=2*i; j<MAX; j+=i){
				isprime[j]=0;
			}
		}
	}
	return;
}

int main()
{
	int n;
	cin>>n;
	sieve();
	int dp[20001];
	fill(dp, dp+n+1, -INF);
	dp[0]=0;
	for(auto x:prime){
		for(int i=n; i>=x; i--){
			dp[i]=max(dp[i-x]+1, dp[i]);
		}
	}
	if(dp[n]>=0) cout<<dp[n]<<endl;
  else cout<<-1<<endl;
	return 0;
}