using System;

public class Program

{

    public static void Main()

    {

        string ids = "1234, 2584, 324234, 2345,45,435,4334,3,456,456,467,568,786,79,3,324,345,464,55,234,4565,8,65,643,637,56,56,34,67";

        int nextIndex = 0;

        while(ids.Length > 0)

        {

            string value = GetString(ids, 20, out nextIndex);

            Console.WriteLine(value);

            ids = ids.Substring(nextIndex);

        }

    }

    private static string GetString(string value, int maxLength, out int nextIndex)

    {

        if(value.Length <= maxLength)

        {

            nextIndex = value.Length;

            return value;

        }

        var v = value.Substring(0, maxLength);

        nextIndex = v.LastIndexOf(",");

        v = v.Substring(0, nextIndex);

        nextIndex += 1;

        return v;

    }

}