Help on The Meeting Place Cannot Be Changed (CodeForce)

Hey guys, this is my first time here so I might make some mistakes writing this, but here the problem is called The Meeting Place Cannot Be Changed, link:
I have been working on it for a while, but I can’t find a good way to determine where they meet at a non-integer point, any hints or tips? Thank you!

IIRC this was in the Binary Search module, so try to think about this from the perspective of binary search.

Try to find whether the friends can meet together in a particular amount of time. Don’t try to binary search on the coordinate point where they meet.