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

using namespace std;

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

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

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

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

int dp[20005] = {-1};
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 (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;
}