Contribution #452

Problem: ru/10.1.20

Added 10.1.20 10.1.21 10.2.4 10.2.5

Editor: Aliaksandr Melnichenka ( @astrosander )

Time: November 6, 2023 at 04:57 PM

GitHub commit: 7b3e3f849068a66ebb4d12b7957f1541f337d3b1

+241 -49 lines changed