Sum Depending On Other Columns

I want to create a macro that make the somme of 2 other columns when the nummer of the first column ist double(more than one ) and put the somme in a new Rows. like this :

A C
23 5
23 12
23 2
45 4
45 1
46 3

in the news the resultat in the same columns it´s like this
A C
23 19
45 5
46 3

I got this code , but I work only for news colums , A and B


Sub test()
Dim a, i As Long, b(), n As Long
a = ActiveSheet. Range("a1"). CurrentRegion.Resize(, 2).Value
Redim b(1 To UBound(a, 1), 1 To 2)
With CreateObject("Scripting.Dictionary")
.CompareMode = vbBinaryCompare
For i = 1 To UBound(a, 1)
If Not .exists(a(i, 1)) Then
n = n + 1: b(n, 1) = a(i, 1)
.Add a(i, 1), n
End If
b(.Item(a(i, 1)), 2) = Val(b(.Item(a(i, 1)), 2)) + Val(a(i, 2))
Next
End With
ActiveSheet.Range("d1").Resize(n, 2).Value = b
End Sub