ZA-SAMO 1995 Problem 5

The convex quadrilateral $ABCD$ has area $1$ , and $AB$ is produced to $E$ , $BC$ to $F$ , $CD$ to $G$ and $DA$ to $H$ , such that $AB=BE$ , $BC=CF$ , $CD=DG$ and $DA=AH$ . Find the area of the quadrilateral $EFGH$ .