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Level 2A

To advance to the next level, you need to solve all problems.

*Additional notes on python

GCD, Euclidean algorithm

Prefix sums and related topics

USACO guide: part one, part two,
Some other theory on prefix sums
You would also need prefix maximums in the problems below.

Recursion

Keep in mind that many of the tasks below are actually easier and more correct to solve not by recursion, but by a loop (in particular, never write factorial or Fibonacci numbers by recursion!). But it is necessary to understand what recursion is, and it is very useful to practice on the tasks below.