#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <map>

using namespace std;

#define INF 		2000000007
#define MOD			1000003

#define MAX 		105

#define REP(i,n)	for(int i=0;i<(n);++i)
#define REPS(i,s,t)	for(int i=(s);i<(t);++i)

typedef unsigned int 			uint;
typedef unsigned long long int	ull;


vector<int> prime(int N){
	int cnt = 1;
	vector<int> pn(N+1);
	REPS(i,N,1) pn[i]=i;
	for(int i=4;i<N;i+=2) pn[i] = -1; 
	for(int i=3;i<N;i+=2){
		if (pn[i]==-1) continue;
		for(int j=i*2;j<=N;j+=i) pn[j]= -1;
		++cnt;
	}
	// 整頓
	vector<int> p(cnt);
	for(int i=0,j=2;j<N;++j){
		if(pn[j]!=-1)p[i++]=j;
	}
	return p;
}

int DP[20005];

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

	vector<int> pn = prime(N+1);// size : 5637

	for(int i:pn) DP[i]=1;

	for(int i:pn){
		//cout << i << endl;
		for(int j=N;j>i;--j){
		//REP(j,N+1){
			if(j-i<=1)continue;
			if(j-i==i)continue;
			if(DP[j-i]==0)continue;
			DP[j] = max(DP[j],DP[j-i]+1);
		}
	}

	cout << (DP[N] > 0 ? DP[N] : -1) << endl;

	return 0;
}