C:\Proj\Version\2014\Planning Summary\Directory of Files

I have 8 sub folders within my "Directory of Files" folder. Each of those 8 sub folders contain 2 other subfolders and some of those 2 other subfolders which contain 50 excel documents each.

I need to have a main excel sheet under my "Planning Summary" Folder that will give me the SUM of each of those individual excel files (that is a lot, i know).

All of the excel files have the same format (they are just copies) and if it helps at all, I am only concerned with the data that is in D37 to AW60. I would like the master workbook to update automatically if any one of those individual documents gets updated. I appreciate the help!