IndexOutOfRangeException

Question

I have a code (at the end). First it goes normal, then goes count of RANDOM sides (not every), and then it goes into mentioned exception. Why is it happening?
https://code.sololearn.com/cjwedW2nSGkD/?ref=app

Answer 1

It works correctly with "for".
https://code.sololearn.com/cX1rWwXOrTsq/?ref=app