//https://yukicoder.me/problems/no/458
//https://yukicoder.me/submissions/203775
#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <vector>
#include <string>
#include <string.h>
using namespace std;

const int MAX_N=20000;
int n;
int dp[MAX_N+1]={};
bool p[MAX_N+1];

int main(){
	cin >> n;
	
	fill(p,p+sizeof(p),true);
	p[0]=false; p[1]=false;
	for(int i=3;i<=n;i++) for(int j=0;j*j<=i;j++){
		if(p[j]){
			if(i%j) continue;
			else p[i]=false;
		}
	}
	
	memset(dp,-1,sizeof(dp));
	dp[0]++;
	for(int i=2;i<=n;i++){
		if(p[i]) for(int j=n;j>=0;j--){
			if(j+i<=n && dp[j]!=-1) dp[j+i] = max(dp[j]+1, dp[j+i]);
		}
	}
	
	cout << dp[n] << endl;
	return 0;
}