If you get the following error message after installing R on your mac:

$ R
dyld: Library not loaded: /usr/local/lib/gcc/5/libgfortran.3.dylib
  Referenced from: /usr/local/Cellar/r/3.2.0_1/R.framework/Versions/3.2/Resources/lib/libR.dylib
  Reason: image not found
Trace/BPT trap: 5

You’ll need to reinstall gcc with the –with-fortran option:

brew reinstall gcc5 --with-fortran