#include <iostream>
#include <cmath>
#include <string>
#include <algorithm>
#include <set>
#include <vector>
#include <map>
#include <list>
#include <stack>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <queue>
#define mkp make_pair
#define pr(num) cout << num << "\n"
#define max(a, b) ((a)>(b) ? (a):(b))
#define min(a, b) ((a)<(b) ? (a):(b))
#define INF 1000000000000000000
#define MOD 1000000007LL
#define MAX 100010
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
typedef map<ll, ll> Map;

vector<ll> primes;

void eratos(ll N) {
    ll isprime[N+5];
    memset(isprime, 1, sizeof(isprime));
    ll i, j;
    isprime[0]=isprime[1]=0;
    for(i=2; i*i<=N; i++) {
        if(!isprime[i]) continue;
        
        for(j=i+i; j<=N; j+=i) {
            if(j%i==0) isprime[j]=0;
        }
    }
    
    for(i=2; i<=N; i++) {
        if(isprime[i]) primes.push_back(i);
    }
    
}


int main() {
    ll N;
    cin >> N;
    ll dp[N+5];
    
    eratos(N);
    memset(dp, -1, sizeof(dp));
    dp[0]=0;
    for(ll p : primes) {
        for(ll i=N; i>=0; i--) {
            if(dp[i]!=-1 && i+p<=N) {
                dp[i+p]=max(dp[i+p], dp[i]+1);
            }
        }
    }
    
    for(ll i=0; i<=N; i++) {
        
    }
    
    
    pr(dp[N]);
}