public class HelloWorld{

    public static void main(String[] args) {

   int one = 10 ;

        int two = 20 ;

        int three = 0 ;

        three = one +two ;

        System.out.println(three);

        three+=one;

        System.out.println(three);

        three*=one;

        System.out.println(three);

        three%=3;

        system.out.println(three);

错误是：error: package system does not exist
system.out.println(three);
^
1 error

老师，怎么回事啊？