import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.TreeSet;

public class Main {
	
	public static long MOD = 1000000007;
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		
		boolean[] is_prime = new boolean[N + 1];
		Arrays.fill(is_prime, true);
		is_prime[0] = is_prime[1] = false;
		
		ArrayList<Integer> primes = new ArrayList<Integer>();
		
		for(int i = 2; i <= N; i++){
			if(!is_prime[i]){ continue; }
			
			primes.add(i);
			for(int j = i * 2; j <= N; j += i){
				is_prime[j] = false;
			}
		}
		
		int[] times = new int[N + 1];
		Arrays.fill(times, -1);
		
		times[0] = 0;
		for(final int p : primes){
			for(int v = N - p; v >= 0; v--){
				if(times[v] < 0){ continue; }
				
				times[v + p] = Math.max(times[v + p], times[v] + 1);
			}
		}
		
		System.out.println(times[N]);
	}
}