Italian Fiscal Code - LastName and FirstName

FiscalCode.cs

class FiscalCode
{
    private static readonly string[] VOC = new string[] { "a", "e", "i", "o", "u" };

    public static string Name(string lastName, string firstName)
    {
        return $"{Lastname(lastName)}{FirstName(firstName)}";
    }

    private static string Lastname(string value)
    {
        var name = value
                // Consonants
                .Where(p => !VOC.Contains(p.ToString(), StringComparer.OrdinalIgnoreCase)).Take(3)
                // Vocals
                .Concat(
                    value.Where(p => VOC.Contains(p.ToString(), StringComparer.OrdinalIgnoreCase)).Take(3)
                )
                // Filler
                .Concat(
                    new char[] { 'X', 'X', 'X' }
                )
                .Take(3)
                .Select(p => p.ToString().ToUpper());

        return string.Join("", name);
    }

    private static string FirstName(string value)
    {
        var cons = value.Where(p => !VOC.Contains(p.ToString(), StringComparer.OrdinalIgnoreCase)).ToArray();

        if (cons.Count() > 3)
        {
            // First, Third and Forth charter
            return string.Join("", new char[] { cons[0], cons[2], cons[3] }.Select(p => p.ToString().ToUpper()));
        }
        else
        {
            // Get all consonants plus all vocals
            var withVocs = cons.Concat(
                value.Where(p => VOC.Contains(p.ToString(), StringComparer.OrdinalIgnoreCase)).Take(3)
                )
                // Filler
                .Concat(
                    new char[] { 'X', 'X', 'X' }
                )
                .Take(3)
                .Select(p => p.ToString().ToUpper());

            return string.Join("", withVocs);
        }
    }
}