There are a total of n delivery points in a delivery station, and these points are connected by m one-way lanes.The delivery person cannot return to a station through a one-way lane. In other words, the n delivery points form a directed acyclic graph. For a delivery point u, if the delivery person can travel from u to any other point v (v≠u), or from v to u, then the station u is considered a super delivery point. Please help calculate the number of super delivery points.

n, m ≤ 3e5