#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <string>
#include <numeric>
#include <cstring>
#include <cmath>
#include <set>
#include <climits>
#include <queue>
#include <stack>

const int MOD = 1e9 + 7;
const int iINF = 1000000000;
const long long int llINF = 1000000000000000000;
#define rep(i, n) for (int i = 0; i < (n); i++)

using namespace std;
using ll = long long int;
using P = pair<int, int>;
using edge = struct
{
    int to;
    int cost;
};

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

bool isPrime[20010];

void Eratosthenes(int N)
{
    memset(isPrime, true, sizeof(isPrime));
    isPrime[0] = false;
    isPrime[1] = false;

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

int dp[20010];

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

    Eratosthenes(N);

    memset(dp, -1, sizeof(dp));

    dp[0] = 0;

    rep(i, N + 1)
    {
        if(isPrime[i])
        {
            for(int j = N; 0 <= j; j--)
            {
                if(i + j > N || dp[j] == -1) continue;

                dp[j + i] = max(dp[j + i], dp[j] + 1);
            }
        }
    }

    cout << dp[N] << endl;

    return 0;
}