Weapon Choice

Chef is playing a videogame, and is now at a boss fight. The boss has $H$ health. Chef has two weapons with him: - First, a gun that does $X$ damage every hit. - Second, a laser that does $Y_1$ damage every hit. However, after the $K$-th time it's used, the laser's output drops; and it will then do only $Y_2$ damage every hit ($Y_2 \lt Y_1$). Chef must choose **exactly one** of the two wea