`end_of_day2.tar.gz` is our `work` directory at the 
end of day2 (Tuesday). This is where we will start from Wednesday.

You can extract it by:

   tar -xzvf end_of_day2.tar.gz

then go to the build directory, configure, build and execute:

   cd end_of_day2/build/
   cmake ../ -DGeant4_DIR=$G4INSTALL/lib64/cmake/Geant4
   make 
   ./yourmain
 
NOTE: there will be a segfault when you execute the program
      which is due to the fact that the G4RunManager is not 
      constructed but used (i.e. nullptr when used in 
      `YourDetectorContruction::SetTargetMaterial` that is 
      invoked from the constructor of `YourDetectorConstruction`). 
      You can correct this by creating the G4RunManager in 
      `yourmain.cc` (just activate the code that is in 
      comment there at lines #4 and #11).