How to import contacts to Outlook Web App Exchange 2013

Hi,

We have deployed Exchange Server 2013. Previously, Our emails were running on a hosted email server. 

Now, our all users are using Outlook Web App to send/receive emails. We had taken the backup of contacts of all users in CSV format from old hosted server. Now, users are looking for their contacts on Outlook Web App. 

Can anyone suggest how to import that old contact to Outlook Web App.

Please help me as it is very crucial for me.

Thanks in advance.