Example graphs are provided in the following format:
n
s_1 t_1
s_2 t_2
…
s_m t_m
The first line contains the number of vertices, n', as a natural
number. Each of the following lines specifies a directed edge in the
form s_i t_i, where s_i is the source vertex and t_i is the
target vertex. Vertices are numbered 0, 1, …, n - 1.