#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <string>
#include <numeric>
#define rep(i, n) for (int i = 0; i < (n); i++)

using ll = long long int;
using namespace std;

bool isPrime[20000] = {false};
int dp[20000];

void eratos(int n)
{

    for (int i = 2; i <= n; i++)
        isPrime[i] = true;

    for (int i = 2; i <= n; i++)
    {
        if (isPrime[i])
        {
            for (int j = 2; i * j <= n; j++)
            {
                isPrime[i * j] = false;
            }
        }
    }

    return;
}

int main()
{
    int N;
    cin >> N;
    eratos(N);
    vector<int> prime;

    rep(i, N + 1)
        dp[i] = -1;

    dp[0] = 0;

    for (int i = 2; i <= N; i++)
        if (isPrime[i])
            prime.push_back(i);

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

    cout << dp[N] << endl;

    return 0;
}