Physics homework problem. polar bear on ice.

A polar bear of mass 510 kg is floating on an iceberg in the ocean. As the ice melts, how small can the iceberg get before the bear gets wet feet? (Your answer should be the volume of the iceberg).

so i made a free body diagram and found that the buoyant force must be equal the the downward weight of the ice and the polar bear. but I'm having a hard time setting up the formula with out having knowing the mass of the ice. I'm not looking for an answer i just need help setting it up. thanks.

The bouyant force equals the weight of the bear "mg" plus the weight of the iceberg "Mg".
Write the weight of the iceberg as density of ice "Di" times total volume "V"
F(bouyant) = mg + DiVg

Next, break up the total volume into submerged volume "Vs" and floating volume "Vf" ;
F(bouyant) = mg + DiVsg + DiVfg

The bouyant force is also equal to the weight of the water displaced by the submerged part of the iceberg;
F(bouyant) = DwVsg

So I would equate these two expressions for F(bouyant) and then solve for Vs when Vf=0.