Option Explicit
Sub ABC()
Dim crit As String
crit = Range("D6")
Dim i As Long
Dim lr As Long, lr2 As Long
Application.ScreenUpdating = False
lr = Range("A" & Rows.Count).End(xlUp).Row
For i = 4 To lr
lr2 = Range("D" & Rows.Count).End(xlUp).Row
If Range("A" & i) = crit Then
Range("D" & lr2 + 1) = Range("B" & i)
End If
Next i
For i = 4 To lr
lr2 = Range("D" & Rows.Count).End(xlUp).Row
If Range("B" & i) = crit Then
Range("D" & lr2 + 1) = Range("A" & i)
End If
Next i
Application.ScreenUpdating = True
End Sub