Print vowel in C#

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication6
{
class Program
{
static void Main(string[] args)
{
string str = "";
Console.WriteLine("\nEnter two numbers");
str= Console.ReadLine();
Console.WriteLine(str);
switch (str.ToLower())
{
case "a":
case "e":
case "i":
case "o":
case "u":

Console.WriteLine("Vowel");
Console.ReadLine();
break;
default:
Console.WriteLine("Not a Vowel");
Console.ReadLine();                    
break;

}       

}
}
}