Let a circle \( C \) in complex plane pass through the point \( z_1 = 3 + 4i \), \( z_2 = 4 + 3i \) and \( z_3 = 5i \). If \( z (\neq z_1) \) is a point on \( C \) such that the line through \( z \) and \( z_1 \) is perpendicular to the line through \( z_2 \) and \( z_3 \), then \( \arg(z) \) is equal to:
