In 12 days the study of any one, or all, of those books will not effect your results in any measurable way.
Moreover, without knowing what your particular strengths and weaknesses are, any advice you get here will simply be personal bias.
Simple Question: What to study first?
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I have a tournament coming up in 12 days. I have 4 books taht i decided to religiously study
1. Mastering chess strategy- Hellsten
2. My System- nimzowitch
3.Complete endgame course- Silman
4. Sharpen your tactics- anatoly lein
In what order should i study these and why? Of course the tactic one i will read in between the other three daily because thats like exercising in between.