#include <iostream>
#include <vector>

using namespace std;

const int MAX = 2e5+1;

bool isprime[MAX];
void era(int N){
    isprime[0] = false;
    isprime[1] = false;
    isprime[2] = true;

    for(int i=1; i<=N;i++){
        if(isprime[i]){
            for(int j=2*i; j<=N;j += i){
                isprime[j] = false;
            }
        }
    }
}

int main(){
    int N; cin >> N;
    fill(isprime, isprime+MAX, true);
    era(200000);
    vector<int> prime;
    for(int i=0;i<=200000;i++){
        if(isprime[i]) prime.push_back(i);
    }

    vector<int> dp(N+1,-1);
    dp[0] = 0;
    for(auto p : prime){
        for(int j=N;j>=0;--j){
            if(p+j <= N && dp[j] != -1){
                dp[j+p] = max(dp[j+p], dp[j]+1);
            }
        }
    }
    cout << dp[N] << endl;
}