Add Digits

using System;
using System.Collections.Generic;

namespace leetcodecsharp
{
    class Program
    {
        public static int AddDigits(int num)
        {
            if (num == 0)
                return 0;
            int i = num;
            while (i.ToString().Length != 1)
            {
                int j = 0;
                foreach (char c in i.ToString())
                    j = j + (int)char.GetNumericValue(c);
                i = j;
            }
            return i;
        }
        public static void Main(string[] args)
        {
            int a = 52515;
            Console.WriteLine(AddDigits(a));
        }
    }
}