#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
#define MAX_N 20001
int N;
int dp[MAX_N + 10][MAX_N + 10];
vector<int> sieve(int n) {
    vector<int> prime;
    vector<bool> is_prime(n + 1, true);
    is_prime[0] = is_prime[1] = false;
    for (int i = 2; i <= n; ++i) {
        if (is_prime[i]) {
            prime.push_back(i);
            for (int j = 2 * i; j <= n; j += i) { is_prime[j] = false; }
        }
    }
    return prime;
}

int main() {
    cin >> N;
    if (N == 1) {
        cout << -1 << endl;
        return 0;
    }
    vector<int> prime   = sieve(N);
    int number_of_prime = prime.size();

    for (int i = 0; i < MAX_N + 10; i++) {
        for (int j = 0; j < MAX_N + 10; j++) {
            if (i <= 1)
                dp[i][j] = 0;
            else
                dp[i][j] = -1;
        }
    }

    for (int i = 0; i <= N; i++) {
        for (int j = 0; j < number_of_prime; j++) {
            if (i - prime[j] >= 0) {
                dp[i][j + 1] = max(dp[i][j], dp[i - prime[j]][j] + 1);
            }
        }
    }

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

    return 0;
}
// dp[i][j]は和がiになるもので、j番目の要素まで使った場合の最大の素数の数
// dp[i][j]=max(dp[i][j-1],dp[i-xj][j-1]+1);