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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        boolean[] isNotPrime = new boolean[n + 1];
        int[] dp = new int[n + 1];
        Arrays.fill(dp, -1);
        dp[0] = 0;
        int max = 0;
        for (int i = 2; i <= n; i++) {
            if (isNotPrime[i]) {
                continue;
            }
            for (int j = 2; j * i <= n; j++) {
                isNotPrime[i * j] = true;
            }
            for (int j = Math.min(max, n - i); j >= 0; j--) {
                if (dp[j] >= 0) {
                    dp[j + i] = Math.max(dp[j + i], dp[j] + 1);
                }
            }
            max = Math.min(max + i, n);
        }
        System.out.println(dp[n]);
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}