Suppose I have an expression which is a collection of symbols and integers arbitrarily combined with Plus and Times. For example, $A = a+c(d - a b d)+e c(a+b)f+b-1$ or maybe $B = a + bacd$ (where $a$, $b$, $c$, $d$, $e$, $f$ are all different symbols), although it could be longer and more complicated. I want to estimate the expression by reducing it to only the terms with zero or one symbol multiplied together because the symbols all represent small numbers, and I want a first-order approximation. E.g. $A \to a+b-1$ and $B \to a$. How can I automate this in Mathematica? Assume that any constants are stand-alone and don't have to be distributed.