For... Next Loop

Hi all, I have a simple code here. Presently, it loops from row 1 to 100. I would like to change it so it loops through the last row of column B that contains data. Thanks all for your help...

Sub Example()
Dim x
    For i = 1 To 100
       x = Cells(i, 1).Select
       Selection.Value = i + 1
    Next i
End Sub