using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

            string value = "4646Y";

​

            Regex regexNumber = new Regex("^[0-9]*Y");

            Match matchNumber = regexNumber.Match(value);

​

        if(matchNumber.Success){

            Console.WriteLine(": {0} {1}", matchNumber);

        }else{

            Console.WriteLine("NO match");

        }

    }

}