  We show that cosmic acceleration can arise due to very tiny corrections to
the usual gravitational action of General Relativity of the form $R^n$, with
$n<0$. This eliminates the need for dark energy, though it does not address the
cosmological constant problem. Since a modification to the Einstein-Hilbert
action of the form $R^n$, with $n>0$, can lead to early-time inflation, our
proposal provides a unified and purely gravitational origin for the early and
late time accelerating phases of the Universe.
