Ants on a Log

You're standing in front of a log that's 100 inches long. You're also holding 4 ants, each of which can walk at a speed of 1 inch per second. You can place the ants anywhere along the log, in either direction, and they will all start walking at the same time. If two ants collide, they will both turn around and walk in the opposite direction.

You start a timer when the ants start walking, and you stop the timer when the last ant falls off the log. You want to maximize this amount of time. How should you place the ants on the log to do this?

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