title: how to convert index to datetime without miliseconds in pandas
body: <p>i have a data frame whose index i want to convert to a datetime format: <code>%Y%m%d%H:%M:%S</code>.
  i have tried the following code: 
  <code>pd.to_datetime(dfn.index,origin=pd.Timestamp('2012-01-01 00:00:00'))</code> </p>
  
  <p>but the DateTime format returned attributed the value of the index to milliseconds as seen.</p>
  
  <p><a href="https://i.stack.imgur.com/8Be9n.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8Be9n.png" alt="enter image description here"></a></p>
  
  <p>When specifying the format, I obtain the error message:
  ValueError: time data '1325376000000000000' does not match format '%Y%m%d%H:%M:%S' (match) </p>
  
  <p>I would like the index value to be attributed to the hours, how can I please do that?</p>
  
  <p>The original data looks like this.</p>
  
  <p><img src="https://i.stack.imgur.com/0X1K3.png" alt="enter image description here"></p>