What does it take to get an S rating?

I just went 15/4/6 as Vayne and I still only got an A+ so do I need to not die at all to get an S? EDIT: Ok, I understand what it takes to get an S now.
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We're testing a new feature that gives the option to view discussion comments in chronological order. Some testers have pointed out situations in which they feel a linear view could be helpful, so we'd like see how you guys make use of it.

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