#include<bits/stdc++.h>

using namespace std;

bool isPrime(int n){
    if(n == 0 || n == 1) return false;
    else if(n == 2 || n == 3 || n == 5) return true;
    else if(n % 2 == 0 || n % 3 == 0 || n % 5 == 0) return false;
    else{
        for(int i=7;i * i <= n;i+=2){
            if(n % i == 0) return false;
        }
    }
    return true;
}

int main(){
    int n;
    cin >> n;
    
    vector<int> prime;
    for(int i=2;i <= 20001;i++){
        if(isPrime(i)) prime.push_back(i);
    }
    
    vector<int> dp(20010,-1);
    dp[0] = 0;
    
    for(auto p: prime){
        for(int j = n;j >= 0;j--){
            if(p + j <= n && dp[j] != -1){
                dp[p+j] = max(dp[p+j],dp[j] + 1);
            }
        }
    }
    
    cout << dp[n] << endl;
}