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

public class DifferentSosu {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int N = s.nextInt();
		s.close();
		ArrayList<Integer> p = new ArrayList<>();
		p.add(2);
		for(int i = 3;i <= N;i++){
			int a = 1;
			for(int j = 0;j < p.size();j++){
				if(i % p.get(j) == 0){
					a = 0;
					break;
				}
			}
			if(a == 1){
				p.add(i);
			}
		}
		//System.out.println(p);
		int[] root = new int[N+1];
		root[0] = 0;
		root[1] = -1;
		for(int i:p){
			for(int j = N;j >= 0;j--){
				if(j-i >= 0&&root[j-i] != -1){
					root[j] = Math.max(root[j-i] + 1, root[j]);
					if(root[j] == 1 && !p.contains(j)){
						root[j] = -1;
					}
				}
			}
			/*for(int k:root){
				System.out.print(k + "  ");
			}
			System.out.println();*/
		}

		System.out.println(root[N]);
		//System.out.println(t.get(N));

	}

}