#include <bits/stdc++.h>
using namespace std;

#define REP(i, m, n) for (int i = (m); i < (int)(n); i++)
#define REPS(i, m, n) for (int i = (m); i <= (int)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define reps(i, n) for (int i = 0; i <= (int)(n); i++)
#define rrep(i, x) for (int i = ((int)(x)-1); i >= 0; i--)
#define rreps(i, x) for (int i = (int)(x); i >= 0; i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
typedef long long ll;
typedef pair<int, int> P;
const int inf = INT_MAX;
const ll INF = 1LL << 60;
const ll mod = 1e9 + 7;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

vector<int> isprime() {
    int MAX = 20010;
    vector<int> is_prime(MAX, 1), p;
    is_prime[0] = 0; is_prime[1] = 0;
    for (int i = 2; i < MAX; i++) {
        if (!is_prime[i]) continue;
        is_prime[i] = i; p.pb(i);
        for (int j = i*2; j < MAX; j += i) is_prime[j] = 0;
    }
    return p;
}

int dp[20010];
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    vector<int> primes = isprime();
    int N; cin >> N;

    fill(dp, dp+N+1, -1);
    dp[0] = 0;

    for (auto p : primes) rreps(i, N) {
        if (p + i <= N && dp[i] != -1) {
            chmax(dp[p+i], dp[i] + 1);
        }
    }
    cout << dp[N] << endl;
    return 0;
}