class Ak
    {
        private string[] _stringArray;

        public Ak(string[] stringArray)
        {
            this._stringArray = stringArray;
        }

        public IEnumerable<Digit> Result()
        {
            //  var result = new List<Digit>();
            foreach (string s in _stringArray)
            {
                string pattern = "^[0-9]";
                Regex regex = new Regex(pattern);
                if (regex.IsMatch(s))
                  yield return new Digit(Convert.ToInt32(s));
            }
            // return result;
        }
        public void Output()
        {
            foreach (Digit d in Result())
            {
                Console.WriteLine(d.ToString());
            }
        }
    }

public static bool Match(this string value, string pattern)
        {
            Regex regex = new Regex(pattern);
            return regex.IsMatch(value);
        }