<image>(2015 Autumn • Jiangxi Final Exam) As shown in the figure in the Cartesian coordinate system, point A moves on the parabola \(y = x^2 - 4x + 6\). Draw a perpendicular line AC from point A to the x-axis at point C. Using AC as the diagonal, a rectangle ABCD is formed. What is the minimum value of the diagonal BD? ____