Dropdown field mus be not the same [RESOLVED]

Dear all,
I have 2 dropdown fields: Country of Departure and Country of Arrival.
These 2 dropdowns have the same country list.
My issue is: I cannot be able to choose the same country of Arrival as the Country of Departure.
If I choose X in the Country of Departure, I cannot be able to choose X in the Country of Arrival.

My second question is do someone know how to do an alert if the same country is chosen in these 2 fields.

Thank you all for your help

J

Please check out this free solution from Gravity Wiz that can help you with this:

Dear Chris.
Thank you very much. It is working really well, exactly as expected.
Best regards