Each face of a cube is painted either red or blue, each with probability $1/2$. The color of each face is determined independently. What is the probability that the painted cube can be placed on a horizontal surface so that the four vertical faces are all the same color? The original answer is in \frac{k}{m} format, please give the value of k + m.

Let's think step by step and output the final answer within \boxed{}.
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