If b=d=1 then r and s can be integers.
We can rewrite the equation:
s=(1-br)/d or r=(1-ds)/b.
So s=1/d-br/d or r=1/b-ds/b.
If d=1, s=1-br, so b must also be an integer.
If b=1, r=1-ds, so d must also be an integer.
If d=1/n, where n is an integer, s=n-nbr so b must also be an integer.
If b=1/m where m is an integer, r=m-mds so d must also be an integer.