#include<algorithm>
#include<cstdio>
#include<iostream>
#include<cmath>
using namespace std;
int N,M;
int i1[20010]={0};
int dp[7500][20010]={0};
int i,j,k,c=0;
int main(void){
	cin>>N;
	i1[c]=2;
	c++;
	for(i=3;i<=N;i+=2){
		k=0;
		for(j=3;j<=sqrt(i);j+=2)
		{
			if(i%j==0)
			{
				k=1;
				break;
			}
		}
		if(k==0){
			i1[c]=i;
			c++;
		}
	}
	for(j=0;j<c;j++){
		for(i=2;i<=N;i++){
			if(dp[j][i-i1[j]]>0||i1[j]==i){
				
				dp[j+1][i]=max(dp[j][i],dp[j][i-i1[j]]+1);
			}
			else{dp[j+1][i]=dp[j][i];}
		}
	}
	if(dp[c][N]==0){cout<<-1<<endl;;}
	else{cout<<dp[c][N]<<endl;}
	return 0;
}