A large computer program is to be tested and debugged in modules, some of which require other modules to be completely tested before testing on them can proceed. The table below shows the dependencies, and the times required to finish the testing and debugging of each module. How long does it take until the entire group of modules is debugged? Do this by hand, rather than with Mathematica.

Module Time (days) Immediate predecessor A B C D E F 122312 none 2 none 2 A 3 B C, D