Among the following expressions, which one is a perfect square? \(\dfrac{14!15!}{2}\), \(\dfrac{15!16!}{2}\), \(\dfrac{16!17!}{2}\), \(\dfrac{17!18!}{2}\), \(\dfrac{18!19!}{2}\). Provide the expression that represents a perfect square in the form \(\dfrac{k!m!}{2}\), and give the value of k + m.

Let's think step by step and output the final answer within \boxed{}.
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