#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

int main() {
    long long n;
    
    cin >> n;

    vector<int> table(n, 1);
    
    for(long long p = 2; p * p < n; ++p){
        if(table[p]){
            for(long long i = p * p; i < n; i += p){
                table[i] = 0;
            }
        }
    }
    
    vector<int> pr;
    for(long long i = 2; i < n; ++i){
        if(table[i]){
            pr.push_back(i);
        }
    }
    
    vector<int> dp(n+10, -1);
    dp[0] = 0;
    
    
    for(int i = pr.size() - 1; i >= 0; --i){
        for(int j = n - pr[i]; j >= 0; --j){
            if(dp[j] != -1){
                dp[pr[i] + j] = max(dp[pr[i] + j], dp[j] + 1);
            }
        }
    }
    

    cout << dp[n] << endl;

    return 0;
}