import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	ArrayList<Integer> primes = new ArrayList<>();
    	int[] counts = new int[n + 1];
    	Arrays.fill(counts, -1);
    	counts[0] = 0;
    	for (int i = 2; i <= n; i++) {
    	    if (isPrime(i, primes)) {
    	        primes.add(i);
    	        for (int j = n - i; j >= 0; j--) {
    	            if (counts[j] < 0) {
    	                continue;
    	            }
    	            counts[j + i] = Math.max(counts[j + i], counts[j] + 1);
    	        }
    	    }
    	}
    	if (counts[n] > 0) {
    	    System.out.println(counts[n]);
    	} else {
    	    System.out.println(-1);
    	}
    }
    
    static boolean isPrime(int x, ArrayList<Integer> primes) {
        for (int y : primes) {
            if (y * y > x) {
                break;
            }
            if (x % y == 0) {
                return false;
            }
        }
        return true;
    }
}