Nested IF ELSE in a derived column

I have the following logic to store the date in my BI_StartDate as below :

• If UpdatedDate is not null then BI_StartDate=UpddatedDate
• ELSE BI_StartDate takes EntryDate value , if the EntryDate is null then BI_StartDate=CreatedDate
• If the CreatedDate IS NULL then BI_StartDate=GetDATE()

I am using a derived column like below :

ISNULL(UpdatedDateODS)? EntryDateODS :(ISNULL(EntryDateODS)? CreatedDateODS :(ISNULL(CreatedDateODS)? GETDATE()))

I am guetting this error :

The expression "ISNULL(UpdatedDateODS) ? EntryDateODS : (ISNULL(EntryDateODS) ? CreatedDateODS :(ISNULL(CreatedDateODS) ? GETDATE() ))" on "Derived Column.Outputs[Derived Column Output].Columns[Derived Column 1]" is not valid.