Do we have to buy SharePoint Server on-premise license even if the organization have E3 subscription

Hello,

Looking for quick response, if someone knows about it.

My question is, do I need to purchase license before installing SharePoint Server even though the organization has Microsoft O365 E3 subscription. I was thinking that once the organization has O365 E3 subscription, then it should cover base and additive CAL equivalents. I means the SharePoint Server Enterprise CAL is an additive CAL, so that use should be covered under Office 365 E3. 

Can anyone please throw some light on it.