Adding values in Column from matching data in another column

Hello,

Im new to this forum so excuse me if my problem is basic or simple but i really am struggling with it.

I want to add the values of one column which correspopnd to the values of another column...

As below i need to read column A then add the corresponding data in B and place the result in column C (

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I really would appreciate any help on how to do this?

Thanks in advance
George

In C1 and copy down,

=IF(A1=A2, "", SUM(INDEX(B:B, MATCH(A1, A:A, 0)):B1))