<image> There is a wooden boat that can seat 20 people and needs to transport 35 students from the shore at point C to islands A and B in the lake for a visit (as shown in the figure). Visiting island A requires 30 minutes, visiting island B requires 20 minutes, sailing between point C and island A takes 10 minutes, sailing between point C and island B takes 12 minutes, and sailing between island A and island B takes 6 minutes. The question is: What is the minimum time required for all 35 students to visit both islands and then return to the shore at point C?