A loop would do it. You have to reset your sum to 0 at the beginning.
Fixed link.
I don't understand. Wouldn't resetting sum every loop index give me the value of the last instance only?
(0) Set SUM to 0, Add Sprite(loopindex).VALUE to SUM
(1) Set SUM to 0, Add Sprite(loopindex).VALUE to SUM
(2) Set SUM to 0, Add Sprite(loopindex).VALUE to SUM
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Like this?