using System;

​

class Person

{

    protected string first_name;

    protected  string last_name;

    protected  int age;

​

    public Person(string ifirst_name, string ilast_name, int iage)

    {

        first_name = ifirst_name;

        last_name = ilast_name;

        age = iage;

    }

​

    public void Greet()

    {

        Console.WriteLine("Hello, " + first_name + " " + last_name + "!");

    }

}

​

class Student : Person

{

    private int grade;

​

    public Student(string ifirst_name, string ilast_name, int iage, int igrade) : base(ifirst_name, ilast_name, iage)

    {

        grade = igrade;

    }

​

    public void Info()

    {

        Console.WriteLine("You are " + age + " years old and you are " + grade + " grade.");

    }

}

​

public class Program

{

  public static void Main(string[] args)

  {

    string first_name = Console.ReadLine();

    string last_name = Console.ReadLine();

    int age = int.Parse(Console.ReadLine());

    int grade = int.Parse(Console.ReadLine());

    Student s = new Student(first_name, last_name, age, grade);

    s.Greet();

    s.Info();

  }

}

​