package no458;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static int INF = 1 << 29;
	public static void main(String[] args) {
		int n = new Scanner(System.in).nextInt();
		ArrayList<Integer> primes = Prime.primeList(20000);
		int[] dp = new int[n+1];
		Arrays.fill(dp, -INF);
		dp[0] = 0;
		for(int p:primes) {
			for(int i=n;i>=p;i--) {
				dp[i] = Math.max(dp[i], dp[i-p] + 1);
			}
		}
		System.out.println(dp[n] < 0 ? -1 : dp[n]);
	}

}
class Prime {
	public static boolean[] isPrimeArray(int max) {
		boolean[] isPrime = new boolean[max+1];
		Arrays.fill(isPrime, true);
		isPrime[0] = isPrime[1] = false;
		for(int i=2;i*i<=max;i++) {
			if (isPrime[i]) {
				int j = i * 2;
				while(j<=max) {
					isPrime[j] = false;
					j += i;
				}
			}
		}
		return isPrime;
	}
	public static ArrayList<Integer> primeList(int max) {
		boolean[] isPrime = isPrimeArray(max);
		ArrayList<Integer> primeList = new ArrayList<Integer>();
		for(int i=2;i<=max;i++) {
			if (isPrime[i]) {
				primeList.add(i);
			}
		}
		return primeList;
	}
}