VBA Program to Compare 4 Columns in Excel (Required)

Hi all

I am New to VBA programming in Excel. Can someone please help me how to create a VBA Program to Compare 4 Columns in Excel and store the values in another column. I have searched it in multiple websites but i couldn't find it. I have got a VBA to compare 2 columns , please let me know how to create it for 4 columns

Private Sub CommandButton1_Click()
Dim CompareRange As Variant, To_Be_Compared As Variant, x As Variant, y As Variant
str1 = InputBox("Enter Column Name to be Compared")
str2 = InputBox("Enter Column Name to Compare")
str3 = InputBox("Enter Column Name to put the Result")
Range(str1 & "1").Select
Selection.End(xlDown).Select
Set To_Be_Compared = Range(str1 & "1:" & Selection.Address)
Range(str2 & "1").Select
Selection.End(xlDown).Select
Set CompareRange = Range(str2 & "1:" & Selection.Address)
i = 1
To_Be_Compared.Select
For Each x In Selection
For Each y In CompareRange
If x = y Then
Range(str3 & i).Value = x
i = i + 1
End If
Next y
Next x
End Sub