An insulating pipe of cross-section area $A$ contains an electrolyte which has two types of ions; their charges being $-e$ and $+2e$. A potential difference applied between the ends of the pipe results in the drifting of the two types of ions, having drift speed $v$ (negative ion) and $v/4$ (positive ion). Both ions have the same number per unit volume $n$. The current flowing through the pipe is