import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		boolean[] isNotPrime = new boolean[n + 1];
		int[] counts = new int[n + 1];
		Arrays.fill(counts, -1);
		counts[0] = 0;
		for (int i = 2; i <= n; i++) {
		    if (!isNotPrime[i]) {
		        for (int j = 2; j * i <= n; j++) {
		            isNotPrime[j * i] = true;
		        }
		        for (int j = n; j - i >= 0; j--) {
		            if (counts[j - i] == -1) {
		                continue;
		            }
		            counts[j] = Math.max(counts[j], counts[j - i] + 1);
		        }
		    }
		}
		System.out.println(counts[n]);
	}
}