summe column depending of other columns

Hi
I have a problem :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 B
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 B
23 19
45 5
46 3

Thanks for your comprehenssion