#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

// 素数判定
bool isPrime(ll n){
    if (n < 2) return false;
    else if (n == 2) return true;
    else if (n % 2 == 0) return false;

    double sqrtNum = sqrt(n);
    for (ll i=3; i<=sqrtNum; i+=2){
        if (n%i == 0){
            return false;
        }
    }
    return true;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N;
    cin >> N;

    vector<ll> primes;
    FOR(i, 2, 20000){
        if(isPrime(i)){
            primes.push_back(i);
        }
    }

    vector<ll> dp(N+1, -1);
    dp[0] = 0;

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

    p(dp[N]);
    
    return 0;
}