#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<ctime>
#include<cctype>
#include<climits>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<memory>
#include<functional>
#include<set>
 
using namespace std;
 
#define ALL(g) (g).begin(),(g).end()
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define F(i,j,k) fill(i[0],i[0]+j*j,k)
#define P(p) cout<<(p)<<endl;
#define INF 1<<25
typedef long long ll;

int dy[8]={1,1,1,0,0,-1,-1,-1};
int dx[8]={-1,0,1,-1,1,-1,0,1};
struct S{
	int a,b,c;
};
bool asc(const S& left,const S& right){
	return left.c > right.c;
}

int N,isprime[20001];
vector<int>prime;
void eratos(int m){
    for (int i = 0; i <= m; ++i) isprime[i] = true;
    isprime[0] = isprime[1] = false;
    for (int i = 2; i <= m; ++i){
        if(isprime[i]){
            for (int j = 2 * i; j <= m; j += i){
                isprime[j] = false;
            }
        }
    }
    for (int i = 2; i <= m; ++i)
        if(isprime[i])prime.push_back(i);
	
}
int main(void){
   	cin >> N;
	vector<int>dp(N+1,-1);
    eratos(20000);
    dp[0] = 0;
    for(auto i : prime){
        for (int j = N; j >= 0; --j){
            if(i+j<=N && dp[j]!=-1){
                dp[i+j]=max(dp[i+j], dp[j] + 1);
            }
        }
		if(i>=N)break;
    }
	cout<<dp[N]<<endl;
    return 0;
}