Articulation Points for Directed Graphs

Hi, I was solving this question at Spoj. - Problem BIA
The question mentions a graph with N vertices and M edges. We want to see if we can cover the entire graph starting from 1, even if we remove the ith vertex. We need to find how many such i exits between 1 and N.
I found an article on the internet as to what I can do , but that works only on undirected Graph as it calculates the articulation points. But I am unable to think of anything for a directed graph. Can you help me regarding which algorithm I should study and implement?