Value of string inputted from textbox

Question

I have a textbox1. If I type ava on textbox1, how to get the value which is 4.

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

Dim ava As Integer = 4

Dim index As Integer = 0

Do
    If index = TextBox1.Text Then
        RichTextBox1.Text = "success"
    End If
    index += 1
Loop Until index > 8

End Sub

try to create a app