#include <iostream>
#include <vector>

using namespace std;

int dp[20005];

vector<int> primes;

bool is_prime(int n)
{
    if (n < 2) return false;

    for (int i = 2; i * i <= n; ++i) {
        if (n % i == 0) return false;
    }

    return true;
}

void init()
{
    int cur = 2; 

    while (cur <= 20000) {
        if (is_prime(cur)) primes.push_back(cur);
        cur++;
    }
}

int main()
{
    init();

    int N; cin >> N;

    for (int i = 0; i <= 20000; ++i) dp[i] = -1;
    dp[0] = 0;

    for (int i = 0; i < primes.size(); ++i) {
        for (int j = 20000; j - primes[i] >= 0; --j) {
            if (dp[j - primes[i]] != -1) {
                dp[j] = max(dp[j], dp[j - primes[i]] + 1);
            }
        }
    }

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