Fibonacci Series in VB 2010

Public Class Form1

Dim P, Q, R, N, I As Integer

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

        ListBox1.Items.Clear()

        P = TextBox1.Text

        Q = TextBox2.Text

        N = TextBox3.Text

        ListBox1.Items.Add("N" & "  Fibonacci Series")

        ListBox1.Items.Add(1 & vbTab & P)

        ListBox1.Items.Add(2 & vbTab & Q)

        For I = 3 To N

            R = P + Q

            P = Q

            Q = R

            ListBox1.Items.Add(I & vbTab & R)

        Next I

End Sub

End Class