Doubt in the code

#1

I was not able to solve the question ,so I opened the solution ,still not able to get anything out of it ,please explain the method to do it in parts so that I can do it.What are the steps to be followed

#2

Just simulate what you have read about the question. How ? Use Sieve of Eratosthenes and store first 10^6 prime numbers, and create stacks dynamically as when you need them.

#3

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