In the description, it first says "N square frames (1 ≤ N ≤ 15) were sequentially drawn on screen". Then it says "However, it should not contain more than 2000 frames".
How many frames are there on screen, 15 or 2000?

I want to ask that, too

would somebody help?

The solution may output more frames than were initially drawn - if two frames overlap and it detects a third frame made from the overlapping parts. It should still be accepted if the total number of frames < 2000.

That said, it shouldn't be a concern if you output at most one frame per input char (i.e., you don't output frames with no reason at all) because there are less input chars than 2000 (20x50 = 1000).

In reference to the problem statement, there are 1 - 15 square frames on the screen and there are 1 - 2000 frames (characters other than dots) on the screen