Native Americans boiled water by adding very hot stones to a leak-tight water vessel.?

What minimum number of 1.0 kg stones at 550 ∘C must be added to a vessel holding 3.0 kg of 20∘C water to bring the water to a boil? Use 800 J/(kg⋅K) for the specific heat of the stones and 4190 J/(kg⋅K) for the specific heat of water.