Complex sentence: Participation in a medical insurance plan with one of the four national insurance funds is compulsory for all citizens, who can select and participate in any one of them regardless of factors such as age, gender, or pre-existing conditions.
Split into simpler sentences: Participation in a medical insurance plan with one of these insurance funds is compulsory for all citizens, who can select and participate in any one of them regardless. Citizens may select any of the four health insurance programs to participate in, regardless of factors such as age or pre-existing conditions.