2.1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _2._1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("How old are you?: ");
            int age = Convert.ToInt32(Console.ReadLine());
            bool isDoorOpen;

            if (age >= 18)
            {
                isDoorOpen = true;
                Console.WriteLine("Welcome!");
            }
            isDoorOpen = false;
        }
    }
}