Use "List Validation" to make one of two columns mandatory

I have the following 3 columns.

• Budgeted: yes or no
• Approver: people field
• Lead_Approver: a dropdown field with emails

What I tried to achieve is when the yes is selected in the Budgeted column, the "Approver" column will be mandatory while no is selected, the "Lead Approver" is mandatory. I could make one mandatory with the statement below but was not sure how to make both happened.

=IF([Budgeted] = False,IF(ISBLANK([Lead_Approver]), false, true),true)

Any help is appreciated. Thanks!

Calvin