5.14. In the pyramid $S A B C$, all faces are equilateral triangles; point $M$ is the center of triangle $A B C$, and point $P$ divides the edge $S C$ in half. Find the decomposition of the vector $\overline{M P}$ in terms of the vectors $\overline{A B}, \overline{A C}$, and $\overline{A S}$.