#include "iostream"
#include "vector"
#include "cmath"
#include "algorithm"

using namespace std;

vector<int> eratos(int n) {
    vector<int> arr(n + 1);

    for (int i = 0; i <= n; i++) arr[i] = 1;

    for (int i = 2; i <= n; i++) {
        if (arr[i] != 0) {
            for (int j = 2; i * j <= n; j++) {
                arr[i * j] = 0;
            }
        }
    }

    vector<int> ret;
    for (int i = 2; i <= n; i++) {
        if(arr[i] != 0) {
            ret.push_back(i);
        }
    }
    return ret;
}

int dp[20010];
int N;

int main() {
    cin >> N;

    vector<int> prime = eratos(N);

    for (int i = 0; i <= N; i++) dp[i] = -1;    
    dp[0] = 0;

    // for (int i = 0; i < prime.size(); i++) {
    //     cout << prime[i] << endl;
    // }

    for (auto elem: prime) {
        for (int i = N; i >= 0; i--) {
            if (elem + i <= N && dp[i] != -1) {
                dp[elem + i] = max(dp[elem + i], dp[i] + 1);
            }
        }
    }
    
    cout << dp[N] << endl;
}