import java.util.*;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.util.Arrays;
import java.util.List;
import java.util.ArrayList;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Collections;
import java.awt.Point;


public class Main {
    public static void main(String[] args) throws Exception {
        
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        List<Integer> primeNums = new ArrayList();
        
        boolean isPrime = true;
        for (int i = 2; i <= n; i++) {
            isPrime = true;
            for (int j = 2; j <= Math.sqrt(i); j++) {
                if (i % j == 0) {
                    isPrime = false;
                }
            }
            if (isPrime) {
                //System.out.println(i);
                primeNums.add(i);
            }
        }
        
        //合計がiとなるときの和の回数の最大値
        int[] dp = new int[n+1];
        dp[0] = 0;
        
        for (int i = 1; i <= n; i++) {
            dp[i] = -1;
        }
        
        for (int p : primeNums) {
            for (int i = n; i >= 0; i--) {
                if (i+p <= n && dp[i] != -1) {
                    dp[i+p] = Math.max(dp[i] + 1, dp[i+p]);
                    //System.out.println("dp " + i + " =" + dp[i]);
                }
            }
        }
        
        
        System.out.println(dp[n]);
    }
}

class Box {
    int w;
    int h;
    public Box(int w, int h) {
        this.w = w;
        this.h = h;
    }
}

class BoxComparator1 implements Comparator<Box>{
	public int compare(Box b1, Box b2) {
		return b1.w - b2.w;
	}
}

class BoxComparator2 implements Comparator<Box> {
    public int compare(Box b1, Box b2) {
        return b1.h - b2.h;
    }
}