In the figure, $A$ and $B$ are the centres of unit circles intersecting each other. Find the area of the region common to both the circles.

In the figure, $A$ and $B$ are the centres of unit circles intersecting each other. Find the area of the region common to both the circles.

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Hint: Connect the intersection points, find the area outside the triangle but inside the sector in one of the circles, then multiply by a factor of 2