using System;

using System.Text.RegularExpressions;                   

public class Program

{

    public static void Main()

    {

          Regex regex = new Regex(@"^-?[0-9][0-9,\.]+$");

                string s;

                do

                {                  

                    Console.WriteLine("Nhap so nguyen co 3 chu so");

                    s = Console.ReadLine();                  

                    if (s.Length == 3 && regex.IsMatch(s))

                    {

                        int tong = Convert.ToInt16(s[0].ToString())

                            + Convert.ToInt16(s[2].ToString());

                        int tich = Convert.ToInt16(s[0].ToString())

                            * Convert.ToInt16(s[2].ToString());

                        Console.WriteLine("Tong & tich so dau va cuoi la: {0} & {1}", tong, tich);

                    }

                    else { Console.WriteLine("Hay nhap so co 3 chu so"); }

                    Console.ReadLine();

                } while (s.Length != 3 || !regex.IsMatch(s));                            

    }

}