You are given an undirected graph consisting of N vertices, numbered from $0$ to N$-1,$ connected with M edges. The graph is described by two arrays, A and B$,$ both of length M$.$ A pair $($A$[$K$],$ B$[$KI$),$ for K from $0$ to M$-1,$ describes an edge between vertex A$[$K$]$ and vertex B$|$K$.$ Each second, every vertex with at most one edge connected to it disappears. Every edge which is connewted to one of the disappearing vertices also disappears. After how many seconds will the vertices stop disappearing? Consider a graph with N $=7$ vertices and following $6$ edges: $(0,1),(1,2),(2,0),(1,4),(4,5)$ and $(4,6).$