This paper is concerned with the impact of a jet of arbitrary cross-section onto a rigid plane. At the initial stage of the impact the liquid motion is described within the framework of the acoustic approximation. Behind the shock front which is generated under the impact, the pressure distribution is calculated analytically for an arbitrary cross-section of the jet. It is shown that a quarter of the total impact energy transfers into the internal energy of the compressed liquid. The focusing of the compression and relief waves in the axisymmetrical case is discussed.