Hi and welcome to the ODK forum, @Roman!
Can you please provide more detail? I think describing more of the workflow here would help. In particular, we'll need to understand what 13 times means in this context.
It's not clear to me what this means.
Again, it would be helpful to get more detail on the workflow. Is there only one data collector? Many? Are the participants being interviewed immediately back to back or is there time between interviews? Are the data collectors always online?
The concept in ODK to use when you need information to be captured between form submissions is the idea of Entities. Entities let you define a way to store state that can be updated by and used by form submissions. In this case you could do something like save a participant entity each time a submission is sent and also attach the entity list to your form so that you can count the number of participant entities registered and make decisions on what should be shown accordingly. Currently entities only work online.
If you have a single data collector, you can store the submission count locally. You can do this with an external counter app or using last saved values. Last saved values are really intended for defaults but some users have had a good experience using it to store things like counters.