Connect AD, then △ BPC △ ADC.

Connecting PD, we get that △PDC is an equilateral triangle AP= 1, AD=√3, PD=2.

So ∠PAD is a right angle.

∠ ADP = 30 (I haven't studied trigonometric functions, but one side of a right triangle is half of the hypotenuse, so the diagonal is 30, you know? )

∠ PDC = 60 equilateral has been proved before.

So ADC = 90 = BPC.

Then use Pythagorean theorem

BC=√7

Circumference 3√7