Let \(N\) be a positive multiple of \(5\). One red ball and \(N\) green balls are arranged in a line in random order. Let \(P(N)\) be the probability that at least \(\tfrac{3}{5}\) of the green balls are on the same side of the red ball. Observe that \(P(5)=1\) and that \(P(N)\) approaches \(\tfrac{4}{5}\) as \(N\) grows large. Find the sum of the digits of the least value of \(N\) such that \(P(N) < \tfrac{321}{400}\).

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