I think I have discovered a formula that answers how many hp we recover when healing in Left 4 Dead. We consider a function, h, that takes numbers in the set {1, 2, 3, ..., 100} and sends them to the set {80, ..., 100}. This function is given by the formula h(n) = 80+f(n/5), where f is the floor function. There is not much to say about the floor function, what it does is take as a result the largest integer below the number we have selected.
Let's see some examples:
a) If n=100, h(100)=80+f(100/5)=80+20=100. This was an expected value, because if we have all the hp, healing would not benefit us at all, in fact, we cannot heal if we have 100 hp.
b) If n=99, h(99)=80+f(99/5)=80+19=99. In this case, healing doesn't help either, we can remember that once we suffer damage, the maximum amount of hp we can aspire to is 99.
c) If n=1, h(1)=80+f(1/5)=80+0=80. This is the least amount of hp we will have after healing.
d) If n=20, h(20)=80+f(20/5)=80+4=84.

Feliz cumpleaños!

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