Assigning Sessions Based on Preference and Seniority Rank

Hopefully you smart Reddit people can help me out with a process I'm having trouble trying to automate.

In the link below you will find a list of students with their name, seniority rank, and preferences for which class session they want to attend ordered by choices 1-5.

https://drive.google.com/folderview?id=0B-nRZcqqlNp_X2g3dDdDZGs2RWM&usp=sharing

I need to find a way to populate the class sessions with the students' highest available preference starting with the lowest seniority rank number (they get first choice). The maximum class size is 3 and if choice #1 is full then they will be assigned their next choice with an opening. If there is no class available that they selected then they are not awarded a class.

I've illustrated how the final product should look at the bottom of the sheet. Hopefully you guys could help me out. I appreciate your time, thanks!