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"Думать".

Yes, this is it. :)
"Думать" is "to think" for everyday usage. "Мыслить" is something like verb for science, philosophy and so on.

"думать" is more wider in usage. You have something in mind which can be: to think, to suppose, to belive, to consider, to guess and similar things.
"мыслить" is "to have brain activity" often...