x = np.arange(1, 51)
l = [100, 500, 1000]
plt.figure(figsize=(18, 8))
for i in range(3):
    plt.plot(x, func1(x, l[i]), label='{} points'.format(l[i]))
plt.grid(True)
plt.legend(prop={'size': 18})
plt.show()