I finally bought doorway pull-up bar, it cost only 15 lats (~21 eur) and was quite easy to setup. No more running half an hour to nearest pull-up bar in forest. I guess I will take a pause from this training program for the sake of variety and will try out some different approaches - like 100 pullups a day or "pyramid" (1-2-3-4-etc). Twenty pullups are still a goal...