```python
import matplotlib.pyplot as plt
import networkx as nx
from dimod.reference.samplers import ExactSolver
from dwave.system.samplers import DWaveSampler
from dwave.system.composites import EmbeddingComposite
import dwave_networkx as dnx
from time import time
from random import shuffle
G = nx.DiGraph()
L = list(range(20))
shuffle(L)
G.add_path(L)
shuffle(L)
G.add_path(L)
nx.draw_networkx(G)
plt.show()
# by CPU 5.9Sec
s = time()
line = dnx.min_vertex_cover(G, ExactSolver())
print(line, "by CPU", round((time()-s), 3), "Sec")