import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;

public class Main {

    void solve() throws IOException {
        int n = ni();

        Prime prime = new Prime(n);
        ArrayList<Integer> primes = prime.primes;

        int m = primes.size();

        long[][] dp = new long[m + 1][n + 1];
        for (int i = 0; i <= m; i++) {
            Arrays.fill(dp[i], -1);
        }
        dp[0][0] = 0;

        for (int i = 0; i < m; i++) {
            int p = primes.get(i);
            for (int j = n; j >= 0; j--) {
                if (dp[i][j] == -1) continue;
                dp[i + 1][j] = dp[i][j];
                if (j + p <= n) {
                    dp[i + 1][j + p] = Math.max(dp[i + 1][j + p], dp[i][j] + 1);
                }
            }
        }

        out.println(dp[m][n]);
    }

    class Prime {
        int n;
        boolean[] isPrime;
        ArrayList<Integer> primes;

        Prime(int n) {
            this.n = n;
            isPrime = new boolean[n + 1];
            primes = new ArrayList<>();
            sieve();
        }

        void sieve() {
            for (int i = 2; i <= n; i++) {
                if (!isPrime[i]) {
                    primes.add(i);
                    for (long j = (long) i * i; j <= n; j += i) {
                        isPrime[(int) j] = true;
                    }
                }
            }
        }
    }

    String ns() throws IOException {
        while (!tok.hasMoreTokens()) {
            tok = new StringTokenizer(in.readLine(), " ");
        }
        return tok.nextToken();
    }

    int ni() throws IOException {
        return Integer.parseInt(ns());
    }

    long nl() throws IOException {
        return Long.parseLong(ns());
    }

    double nd() throws IOException {
        return Double.parseDouble(ns());
    }

    String[] nsa(int n) throws IOException {
        String[] res = new String[n];
        for (int i = 0; i < n; i++) {
            res[i] = ns();
        }
        return res;
    }

    int[] nia(int n) throws IOException {
        int[] res = new int[n];
        for (int i = 0; i < n; i++) {
            res[i] = ni();
        }
        return res;
    }

    long[] nla(int n) throws IOException {
        long[] res = new long[n];
        for (int i = 0; i < n; i++) {
            res[i] = nl();
        }
        return res;
    }

    static BufferedReader in;
    static PrintWriter out;
    static StringTokenizer tok;

    public static void main(String[] args) throws IOException {
        in = new BufferedReader(new InputStreamReader(System.in));
        out = new PrintWriter(System.out);
        tok = new StringTokenizer("");
        Main main = new Main();
        main.solve();
        out.close();
    }
}