x = [1, 2, 3, 4, 5]
y1 = [1, 2, 3, 4, 5]
y2 = [5, 4, 3, 2, 1]

plt.plot(x, y1, label='Ascending')
plt.plot(x, y2, label='Descending')
plt.legend()
plt.title('Adding a Legend')
plt.show()