Given the task definition and input, reply with output. In this task, you're given passages that contain mentions of a time duration related quesry and we are supposed to write answer to a question that involves event “frequency", which refers to how often an event is likely to be repeated. For example, "taking showers" typically occurs ~5 times a week, "going to saturday market" usually happens every few weeks/months, etc. 
 Note that a lot of the questions could have more than one correct answers. We only need a single most-likely answer. Please try to keep your "answer" as simple as possible. Concise and simple "answer" is preferred over those complex and verbose ones.  

Sentence: Every year a "Brotherhood and Unity" relay race is organized in Montenegro, Macedonia and Serbia which ends at the "House of Flowers" in Belgrade on May 25 – the final resting place of Tito. At the same time, runners in Slovenia, Croatia and Bosnia and Herzegovina set off for Kumrovec, Tito's birthplace in northern Croatia. The relay is a left-over from Yugoslav times, when young people made a similar yearly trek on foot through Yugoslavia that ended in Belgrade with a massive celebration. 
Question: How often is the "Brotherhood and Unity" relay race done?

Every year