Certain profile cannot change 'Assigned To'

[tuscani6]

Can anyone please help with creating a validation rule that prevents a certain Profile Name from being able to change the "Assigned To' field.  All other profile names should be able to change the 'Assigned To' unless Profile = 'C User'

[phiberoptik]

AND(
    ISCHANGED(OwnerId ), 
    $User.ProfileId = "Enter Profile Id for Profile C User" 
)