I am quite confused with boolean algebra and I have to simplify this:

SF + PB + DM + DB = 1

Would the simplification process be:

SF + PB + DM + DB = 1

SF + PB + D(M + B) = 1

SF + PB + B(M + D) = 1

SF + B(P +M + D) = 1

is this correct? If not, could you explain where I've gone wrong? thanks,

Ollie