I have a folder with a number of identical workbooks each one saved under a
different department.

Each workbook contains 13 worksheets identified as Wk1 to Wk13 representing
13 weeks

In week 13 I wish to identify in cell P5 the total of the contents of cell
M5 in each of the 13 worksheets. I have tried several formulations but I
either get an error message or it brings up the folder with all the workbooks
as if I have hit the open icon.
Each of the M5 cells will only have a number in it.

Any help would be appreciated--
with kind regards
Mick