  By setting some special boundary conditions in the variational principle we
obtain junction conditions for the five-dimensional $f(R)$ gravity which in the
Einstein limit $f(R)\rightarrow R$ transform into the standard Randall-Sundrum
junction conditions. We apply these junction conditions to a particular model
of a Friedmann universe on the brane and show explicitly that the limit gives
the standard Randall-Sundrum model Friedmann equation.
