using System;

using System.Collections.Generic;

using System.Linq;

​

public class PersonDTO

{

    public int Id { get; set; }

    public string Name { get; set; }

    public int Age { get; set; }

}

​

public class PersonService

{

    private List<PersonDTO> people = new List<PersonDTO>();

​

    // Add a new person to the list

    public void AddPerson(PersonDTO person)

    {

        people.Add(person);

    }

​

    // Remove a person from the list by Id

    public bool RemovePerson(int id)

    {

        var person = people.FirstOrDefault(p => p.Id == id);

        if (person != null)

        {

            people.Remove(person);

            return true;

        }

        return false;

    }

​

    // Get people by a specific age

    public List<PersonDTO> GetPeopleByAge(int age)

    {

        return people.Where(p => p.Age == age).ToList();

    }

​

    // Get all people

    public List<PersonDTO> GetAllPeople()

    {

        return people.ToList();

    }

}

​

class Program

{

    static void Main()

    {

        PersonService service = new PersonService();

        // Add some people

        service.AddPerson(new PersonDTO { Id = 1, Name = "Alice", Age = 30 });

        service.AddPerson(new PersonDTO { Id = 2, Name = "Bob", Age = 25 });

        service.AddPerson(new PersonDTO { Id = 3, Name = "Charlie", Age = 30 });

​

        // Remove a person

        service.RemovePerson(2);

​

        // Get people by age

        var peopleAge30 = service.GetPeopleByAge(30);

        Console.WriteLine("People aged 30:");

        foreach (var person in peopleAge30)

        {

            Console.WriteLine($"{person.Name}, {person.Age}");

        }

        Console.WriteLine();

        // Get all people

        var allPeople = service.GetAllPeople();

        Console.WriteLine("All people:");

        foreach (var person in allPeople)

        {

            Console.WriteLine($"{person.Name}, {person.Age}");

        }

    }

}