#include <bits/stdc++.h>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<long double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<string> vs;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<int,P> pip;
typedef vector<pip> vip;
const int inf=1<<30;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-8;
const ll mod=1e9+7;
const int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};

int n;
vi p,dp;

int main(){
	cin>>n;
	p=vi(n+1,1);
	dp=vi(n+1,-inf);
	dp[0]=0;
	for(int i=2;i<=n;i++) if(p[i]){
		for(int j=2*i;j<=n;j+=i) p[j]=0;
		for(int j=n;j>=i;j--) dp[j]=max(dp[j],dp[j-i]+1);
	}
	if(dp[n]<0) cout<<-1<<endl;
	else cout<<dp[n]<<endl;
}