What would be the answer to Prob. 22 if only the five

What would be the answer to Prob. 22 if only the five ships S1, · · ·, S5 had to be accommodated?

Data from Prob. 22

How many piers does a harbor master need for accommodating six cruise ships with expected dates of arrival A and departure D in July, (A, D) = (10, 13), (13, 15), (16, 18), (14, 17), (12, 15), (16, 18), (14, 17), respectively, if each pier can accommodate only one ship, arrival being at 6 am and departures at 11 pm? Join Si and Sj by an edge if their intervals overlap. Then color vertices.

PROBLEM SET 23.3: