If some clouds are black and it's humid, then it will rain.

I have it notated as follows:

C(-s-)B + H -> R

My question is - can you even take a contrapositive of this statement?

And if so, is it the following:

/R -> /H or C->/B

In other words:

If it is not raining, then it means either it is not humid or all clouds are not black...

Am i correct in thinking this?