Two runners (Mr. A and Mr. B) stand exactly 10 miles apart. A fly rests on Mr. A's chest. The two men run straight toward each other (each running at 5 miles per hour), and at the same moment the fly flies off of Mr. A heading straight toward Mr. B at 8 miles per hour. When the fly reaches Mr. B, it immediately turns around and flies back toward Mr. A. The fly continues to reverse directions every time it reaches one of the runners. How far will the fly have traveled when the two runners smash into each other? Assume that all three of them maintain constant speeds.