import java.util.*;
import java.io.*;

public class Main {
    static int size;
    static int[][] dp;
    static ArrayList<Integer> primes = new ArrayList<>();
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        for (int i = 2; i <= n; i++) {
            if (isPrime(i)) {
                primes.add(i);
            }
        }
        size = primes.size();
        dp = new int[size][n + 1];
        int ret = dfw(size - 1, n);
        if (ret <= 0) {
            System.out.println(-1);
        } else {
            System.out.println(ret);
        }
    }
    
    static int dfw(int idx, int num) {
        if (num == 0) {
            return 0;
        }
        if (idx < 0) {
            return Integer.MIN_VALUE;
        }
        if (dp[idx][num] != 0) {
            return dp[idx][num];
        }
        int ret = dfw(idx - 1, num);
        int now = primes.get(idx);
        if (num >= now) {
            ret = Math.max(ret, dfw(idx - 1, num - now) + 1);
        }
        dp[idx][num] = ret;
        return ret;
    }
    
    static boolean isPrime(int num) {
        for (int x : primes) {
            if (Math.sqrt(num) < x) {
                break;
            }
            if (num % x == 0) {
                return false;
            }
        }
        return true;
    }
}