The thermal conductivity of the fur (including the skin) of a male Husky dog is 0.026 W/(m ∙ K). The dog's heat output is measured to be 51 W, its internal temperature is 38°C, its surface area is 1.31 m2, and the thickness of the fur is 5.0 cm. How cold can the outside temperature be before the dog must increase its heat output?