The value of the expression $$\cos^{2} 45^{\circ} + \cos^{2} 135^{\circ} + \cos^{2} 225^{\circ} + \cos^{2} 315^{\circ}$$ is:

A

2

B

$$\frac{1}{2}$$

C

$$\frac{2}{3}$$

D

1