#include <bits/stdc++.h>

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define RFOR(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep1(i, n) for (int i = 1; i <= (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)

#define pb push_back
#define mp make_pair
#define fst first
#define snd second
#define show(x) cout << #x << " = " << x << endl
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define pii pair<int, int>
#define vi vector<int>

using namespace std;
template <class S, class T>
ostream& operator<<(ostream& o, const pair<S, T>& p)
{
    return o << "(" << p.first << "," << p.second << ")";
}
template <class T>
ostream& operator<<(ostream& o, const vector<T>& vc)
{
    o << "sz = " << vc.size() << endl
      << "[";
    for (const T& v : vc)
        o << v << ",";
    o << "]";
    return o;
}
using ll = long long;
constexpr ll MOD = 1000000007;

constexpr int MAX = 20000;

bool check[MAX + 1];
int dp[MAX + 1];
vector<int> prime;

int main()
{
    int N;
    cin >> N;
    for (int i = 2; i <= N; i++) {
        check[i] = true;
    }
    for (int i = 0; i <= N; i++) {
        dp[i] = -1;
    }
    for (int i = 2; i <= N; i++) {
        if (check[i]) {
            prime.pb(i);
            for (int j = 2; i * j <= N; j++) {
                check[i * j] = false;
            }
        }
    }
    dp[0] = 0;
    for (int p : prime) {
        for (int i = N - p; i >= 0; i--) {
            if (dp[i] != -1) {
                dp[i + p] = max(dp[i + p], dp[i] + 1);
            }
        }
    }
    cout << dp[N] << endl;

    return 0;
}