class Program    {        static void Main(string[] args)        {            string s = Sum("abc", "abc"); // 1134            Console.WriteLine(s);            Console.Read();        }        /// 
        /// 二十进制相加        /// 
        /// 字符串a        /// 字符串b.        /// 
             static string Sum(string a, string b)        {            int len = a.Length > b.Length ? a.Length + 1 : b.Length + 1;            char[] ar = new char[len];            int i = 0;            int ai = a.Length - 1;            int bi = b.Length - 1;            int t;            int ad = 0;            while (ai >= 0 || bi >= 0)            {                if (ai >= 0 && bi >= 0)                {                    t = Map(a[ai]) + Map(b[bi]) + ad;                }                else if (ai >= 0)                {                    t = Map(a[ai]) + ad;                }                else                {                    t = Map(b[bi]) + ad;                }                ar[i++] = RMap(t % 20);                ad = t / 20;                ai--;                bi--;            }            if (ad > 0)            {                ar[i] = '1';            }            int h = ar.Length - 1;            while (ar[h] == '\0')            {                h--;            }            string s = "";            while (h >= 0)            {                s += ar[h--];            }            return s;        }        /// 
        /// Maps the specified c.        /// a -> 10 , j-> 19 , others exception        /// 
        /// The c.        /// 
             /// 
     
      c
             static int Map(char c)        {            c = char.ToLower(c);            if (c >= 'a' && c <= 'j')            {                return 10 + (c - 'a');            }            throw new ArgumentException("c");        }        /// 
        ///Map int to char, 10 -> a , 19 -> j        /// 
        /// The i.        /// 
             /// 
     
      i
             static char RMap(int i)        {            if (i >= 10 && i <= 19)            {                return Convert.ToChar(87 + i);            }            else if (i < 10)            {                return i.ToString()[0];            }            throw new ArgumentException("i");        }    }