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

B = a + b a c d
``` 
(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:

```
Ar = a + b - 1

Br = a
``` 

How can I automate this in Mathematica? Assume that any constants are stand-alone and don't have to be distributed.