Starting at value 0 , the profit of an investor increases per week by \(\$ 1\) with probbability \(p, p>1 / 2\), or decreases per week by one unit with probability \(1-p\). The weekly increments of the investor's profit are assumed to be independent. Let \(N\) be the random number of weeks until the profit reaches for the first time a positive integer \(n\). By means of Wald's equation, determine \(E(N)\).