5. Given a convex quadrilateral $ABCD$ with area $S$, $O$ is a point outside the quadrilateral, $M_{1}, M_{2}, M_{3}, M_{4}$ are the centroids of $\triangle OAB$, $\triangle OBC$, $\triangle OCD$, $\triangle ODA$ respectively. Then the area of quadrilateral $M_{1} M_{2} M_{3} M_{4}$ is $\qquad$
5. $\frac{2}{9} S$.

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