For p, q, ∈ R, consider the real valued function \(f(x) = (x – p)^2 – q\), x ∈ R and q > 0, Let \(a_1, a_2, a_3\) and \(a_4\) be in an arithmetic progression with mean p and positive common difference. If |f(ai)| = 500 for all i = 1, 2, 3, 4, then the absolute difference between the roots of f(x) = 0 is