[asy]
unitsize(1 cm);
draw(Circle((0,0),1));
draw(Circle((1,0),1));
draw(Circle((0.5,0.87),1));
label("$A$", (-0.5,0), W);
label("$B$", (1.5,0), E);
label("$C$", (0.5,1.7), N);
filldraw(arc((0,0),1,0,180)--arc((1,0),1,180,360)--cycle, gray(0.7));
[/asy]
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