How to correctly compose an algorithm for the prepositions `v` and `vo`?

Question

Algorithms

Example:
We have a category of tours called Tours . Countries may have different categories of tours. example:

• EXCURSION TOURS TO FRANCE
  
• EXCURSION TOURS TO RUSSIA
  
• EXCURSION TOURS TO NORWAY
  
• EXCURSION TOURS TO VIETNAM
  

Wrote a library for countries from single to plural. Now the task is to write a library for prepositions in and in , but I don’t know what to catch on here. Throw ideas please.

Answer 1

new.gramota.ru/spravka/buro/search-answer?s=233445
Regular expressions can be dispensed with here