#include <bits/stdc++.h>
using namespace std;
 
#define rep(i,a,b) for(int i=a;i<b;i++)
typedef long long ll;
const ll inf = 100100100100100;

vector<int> eratosthenes(int n){
    int arr[n+1];
    rep(i,0,n+1){
        arr[i] = 1;
    }
    arr[0] = 0; arr[1] = 0;
    for(int i = 2; i < n; i++){
        if(arr[i]==1){
            for(int j = 2*i; j < n+1; j+=i){
                arr[j] = 0;
            }
        }
    }
    
    vector<int> ret;
    for(int i = 2; i<n+1; i++){
        if(arr[i] == 1){
            ret.push_back(i);
        }
    }
    return ret;

}

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

    int n; cin >> n;

    vector<int> primes = eratosthenes(n);
    
    int dp[n+1]; rep(i,0,n+1) dp[i] = -1;
    dp[0] = 0;

    for(auto e : primes){
        for(int i = n; i > -1; i--){
            if(i + e < n+1 && dp[i] > -1){
                dp[i+e] = max(dp[i+e], dp[i] + 1); 
            }
        }
    }

    cout << dp[n] << endl;

}