I've installed mist and considered that I don't remember the password from wallet that attached to it. Which operation should I launch to start brutforcing the password?
If I understand your problem: You installed Mist and created wallet some time ago. Now you still have access to that installed Mist, but you are not sure if you remember the password. If I'm right try below:
Create another account in e.g. myetherwallet.com and try to send some Ether to that account from the Mist wallet.
Other (maybe a bit simpler way) is to run, this easy example Dapp in your Mist browser, when you will try to vote, Mist will request a password. If you succeed you will spend just pennies on gas. https://ethereum.github.io/stake-voice/