I need help guys. I know its simple but I have no clue how its done.

I have two circles, with the same radius, R, and I offset one by a distance X from the origin ( take the center of one of the circles as the origin). I need to calculate the area of the overlapping region. Since the two have the same radii, I assume that it shouldn't be thta complicated, but i'm completely STUCK and can't think ! :S

Thanks guys,