#include <iostream>
#include <cmath>
#include <vector>

using namespace std;
using LL = long long;
using ULL = unsigned long long;

int main() {
    int N;
    cin >> N;

    bool P_[N + 1];
    for (bool &p: P_) p = true;

    P_[0] = false;
    P_[1] = false;
    for (int i = 2; i <= sqrt(N); i++) {
        if (P_[i]) {
            for (int j = i * 2; j <= N; j += i) {
                P_[j] = false;
            }
        }
    }

    vector<int> P;
    for (int i = 0; i <= N; i++) {
        if (P_[i]) P.push_back(i);
    }

    //
    int dp[N + 1];
    for (int &i: dp) i = -1;

    dp[0] = 0;
    for (int i = 0; i < P.size(); i++) {
        for (int j = N - P[i]; j >= 0; j--) {
            if (dp[j] != -1) dp[j + P[i]] = max(dp[j + P[i]], dp[j] + 1);
        }
    }

    cout << dp[N] << endl;
}