It is for free in Humble Bundle: https://www.humblebundle.com/mission/summer-sale-rewards?hmb_source=store_home
You have to only visit Humble Store one per day to collect one stamp.

6 years ago
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Thank you very much!! :)

6 years ago
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thank you!!

6 years ago
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This comment was deleted 6 years ago.

6 years ago
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You're welcome :)

6 years ago
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