If triangles ABC and PQR are both isosceles with AB=AC and PQ=PR, respectively. If also AB=PQ and BC=QR and angle $$B=50^{\circ}$$, then what is the measure of angle R?

A

$$50^{\circ}$$

B

$$80^{\circ}$$

C

$$90^{\circ}$$

D

$$60^{\circ}$$