就是找规律，从第三个开始都是有规律的 
import java.util.*;

public class Main{
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int num = sc.nextInt();
            int a=0;
            if(num==1||num==2){
                a=-1;
            }else{
                switch((num-2)%4){
                    case 0:
                        a=4;
                        break;
                    case 1:
                        a=2;
                        break;
                    case 2:
                        a=3;
                        break;
                    case 3:
                        a=2;
                        break;
                }
            }
            System.out.println(a);
        }
    }
}