using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var regex = new Regex(@"(^[0-9]{11,11}$)|(^[0-9]{9,9}V$)", RegexOptions.Compiled);

        var input1 = "359123404V";

        var input2 = "19924578124";

        // no match

        var input3 = "1992457812481";

        var input4 = "359123404v";

        Console.WriteLine("Matches " + input1 + ": " + regex.IsMatch(input1));

        Console.WriteLine("Matches " + input2 + ": " + regex.IsMatch(input2));

        Console.WriteLine("Matches " + input3 + ": " + regex.IsMatch(input3));

        Console.WriteLine("Matches " + input4 + ": " + regex.IsMatch(input4));

    }

}