316. The Fly's Journey. A fly, starting from point $A$, can travel around the four sides of the base of a cube in 4 minutes. How long will it take to reach the opposite vertex $B$?

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316. A smart fly would choose the path marked on the diagram with a solid line, and it would take 2.236 minutes to overcome it. The path marked with a dashed line is longer, and it would take more time.

![](https://cdn.mathpix.com/cropped/2024_05_21_56f37ca27ac3d928838dg-255.jpg?height=423&width=397&top_left_y=2027&top_left_x=841)