  We study electron pumping through a system of barriers, whose heights are
deformed adiabatically. We derive a simple formula for the pumped charge $Q$ in
terms of the total reflection and transmission amplitudes and phases. The
pumped charge increases with the number of barriers ($n_b$) and shows an
interesting step-like behaviour, with the steps appearing at integer values of
$Q$. The pumped charge also tends towards quantisation with the increase of the
amplitude of the time-varying potential. The value of the quantised pumped
charge is shown to be correlated to the discontinuity of the reflection phase.
