How can I determine my oldest log

Hi Guys,

Does anyone have an easy method for finding the oldest log for a device on the FortiAnalyzer?  I'm adjusting quotas and I want to be sure I have a sufficient log retention.  

I know you can go into log browse and view the dates on the files there but I would prefer to do it via the CLI or some other more repeatable method.  I know I'm asking for a  lot but it would be awesome if there was a report that could produce this info!