How to arrange flex blocks?

Question

Flexbox

Hello, I am just starting to work closely with flex. And I just can’t figure out how to do this https://yadi.sk/i/jwQR5-vkuk38i
The difficulty is that this is a UL list with a structure

<ul>
   <li>nth-child(1)</li>
   <li>nth-child(2)</li>
   <li>nth-child(3)</li>
</ul>

How to make the blocks stand up like on the screen?

Answer 1

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