java developer makes a C# program (colorized)

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
public class Program
{
    private static readonly Regex regex = new Regex(@"^\d+$");
    public static void Main()
    {
        List<String> toSend = new List<String>();
        String ae = "";
        Console.WriteLine("Enter a number!!!! (!!!)");
        String a = Console.ReadLine();
        if (!regex.IsMatch(a)) {
            Console.WriteLine("That isnt a number!");
            return;
        }
        int b = Int32.Parse(a);
        Console.WriteLine("You specified: " + a + " a's! I will now print them!");
        for (int i = 0; i < b; i++) {
            toSend.Add("a");
        }
        ae += "[";
        foreach (String s in toSend) {
                ae+="\"a\", ";
        }
        ae = ae.Substring(0, ae.LastIndexOf(","));
        ae += "]";
        Console.WriteLine(ae + "\nDone!!!!!!!!!!!!!");
    }
}