Format timestams on x axis using matplotlib

[igorv]

How to show timestamps on x axis as "%Y-%m-%d %H:%M". ts is list of timestamps and how to show on x axis only values "2018-5-23 14:00", "2018-5-23 14:15" and "2018-5-23 14:30".
My current chart shows: 23 14:00, 23 14:05, 23 14:10, 23 14:15, 23 14:20, 23 14:25, 23 14:30.
Chart

import datetime
import matplotlib.pyplot as plt
from matplotlib import style
style.use('fivethirtyeight')

ts = [datetime.datetime(2018, 5, 23, 14, 0), datetime.datetime(2018, 5, 23, 14, 15), datetime.datetime(2018, 5, 23, 14, 30)]
values =[3, 7, 6]
plt.plot(ts, values, 'o-')
plt.show()