proverka na email

 static void Main(string[] args)
        {
            //проверка за валиден имеил
            string email = Console.ReadLine();
            int b = email.IndexOf("@");
            int br = 0;
            bool flag = true;
            Console.WriteLine(b);
            if (b > -1)
            {
                for (int i = b + 1; i < email.Length; i++)
                {
                    if (email[i] == '.')
                        br++;
                }
                for (int i = 0; i < b; i++)
                {
                    if (!(email[i] >= 'a' && email[i] <= 'z') && !(email[i] >= '0' && email[i] <= '9') && !(email[i] == '.') && !(email[i] == '_'))
                    {
                        flag = false; break;
                    }

                }
                if (br == 0)
                    Console.WriteLine("nevaliden email server ");
                if (flag == false)
                    Console.WriteLine("nevalidno potrebitelsko ime");
                if (br > 0 && flag)
                    Console.WriteLine("validen email");
            }
         else Console.WriteLine("nevaliden email");
        }