#include <iostream>
#include<vector>

using namespace std;

vector<int> primes;


int main(){
    int count[20001];
    count[0] = 0;
    primes.push_back(2);
    for(int i=3;i<20000;i+=2){
        for(int j=0;j<primes.size();j++){
            if(i%primes[j]==0)break;
            if(j == primes.size()-1)
            primes.push_back(i);
        }
    }

    int N;
    cin>>N;
    for(int i=0;i <=N;i++){
        count[i]=-1;
    }
    count[0]=0;
    for(int i=0;i<primes.size();i++){
        for(int j=N;j>=0;j--){
            if(count[j]!=-1&&j+primes[i]<=N){
                count[j+primes[i]] = max(count[j+primes[i]],count[j]+1);
            }
        }
    }

    cout<<count[N];
}