#include<bits/stdc++.h>
#define ALL(v) std::begin(v),std::end(v)
using lint=long long;
using lubl=long double;
void cmx(lint&x,lint y){if(x<y)x=y;}
int main(){
    std::cin.tie(nullptr);std::ios_base::sync_with_stdio(false);
    std::cout.setf(std::ios_base::fixed);std::cout.precision(15);
    lint n;std::cin>>n;
    std::vector<lint>primes;
    std::vector<lint>sieve(n+1,false);
    for(lint p=2;p<=n;p++){
        if(sieve.at(p))continue;
        primes.push_back(p);
        for(lint i=p*p;i<=n;i+=p)sieve.at(i)=true;
    }
    std::vector<lint>dp(n+1,-1);
    dp.at(0)=0;
    for(lint p:primes){
        for(lint i=n-p;i>=0;i--){
            if(dp.at(i)==-1)continue;
            cmx(dp.at(i+p),dp.at(i)+1);
        }
    }
    std::cout<<dp.at(n)<<'\n';
}