#include <bits/stdc++.h> 
using namespace std;
#define FOR(i,l,r) for(size_t i=(l); i<(r); i++)
#define REP(i,n) FOR(i,0,n)
#define endl "\n"
#define debug(x) cout<<x<<endl;
typedef long long ll;
static const int MOD = 1e9+7;
static const ll INF = 1ll<<60;

vector<int> Eratosthenes(int N){
    vector<int> prime(N+1,true);

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

    vector<int> res;

    REP(i,N+1){
        if(prime[i]){
            res.push_back(i);
        }
    }

    return res;
}

int main(){
    int N;
    cin>>N;
    vector<int> prime = Eratosthenes(N);
    vector<int> dp(N+1,-1);
    dp[0] = 0;

    for(auto i : prime){
        for(int j=N; j>=0; j--){
            if(j - i < 0) continue;
            if(dp[j-i] == -1) continue;
            dp[j] = max(dp[j],dp[j-i]+1);
        }
    }

    cout<<dp[N]<<endl;

    return 0;
}