import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        boolean [] b = new boolean [N+1];
        ArrayList<Integer> prime = new ArrayList<Integer>();
        prime.add(2);
        for(int i=3; i<=N; i+=2){
            if(b[i]==false){
                prime.add(i);
                int k=2;
                while(i*k<=N){
                    b[i*k]=true;
                    k++;
                }
            }
        }
        boolean [] dp = new boolean [N+1];
        dp[0]=true;
        int [] num = new int [N+1];
        for(int i=0; i<prime.size(); i++){
            int t=prime.get(i);
            for(int j=N; j>=0; j--){
                if(dp[j]){
                    int tmp=j+t;
                    if(tmp<=N){
                        dp[tmp]=true;
                        num[tmp]=Math.max(num[tmp],num[j]+1);
                    }
                }
            }
        }
        int ans=num[N];
        if(ans==0)ans=-1;
        System.out.println(ans);
    }
}