The problem is 1041F - Ray in the tube
These words are copied from the problem:
To do so, you have to choose two integer points A and B on the first and the second line respectively (coordinates can be negative): the point A is responsible for the position of the laser, and the point B — for the direction of the laser ray. The laser ray is a ray starting at A and directed at B which will reflect from the sides of the tube (it doesn't matter if there are any sensors at a reflection point or not). A sensor will only register the ray if the ray hits exactly at the position of the sensor.
I think A and B only have to be integers, but it doesn't say they cannot be a straight line.
B as the direction, it even can out of the tube.
And my submission got Wrong Answer on test 51. (Submission : 43024618)
After the Virtual Participation, I got the test of test 51, and found n = 12000 and m = 32000
So I think the answer should be 32000, instead of 24000 (Submission : 43065546)
Because I can use a single line with A(-2,y2) and B(-1,y2) to get 32000 points instead of 24000.