One of the reasons for which École polytechnique (nicknamed ``X" for reasons to be explained during the debriefing talk) is so deeply rooted in French society is its famous network of camarades - former students of the same school. When one camarade wants something (money, job, etc.), he can ask this network for help and support. In practice, this means that when he/she wants to reach some other camarade, not always of the same year, then surely he can find intermediate camarades to get to her/him. Note that the ``camarade" relationship is symmetric. Due to the magic of the X network, there is always a means to reach anybody.
The program you have to write is supposed to help to minimize the number of these intermediate camarades.