Exclude the CEO from supervisory approval hierarchy

Appreciate your assistance to guide us in the below issue regarding BPM approval rule in individual compensation.

we have applied a 3 level approval flow in supervisory hierarchy in the individual compensation approval rule.

but if the 'CEO' comes in the approval hierarchy (first line manager or second or third) we want to skip him.

i tried the below expression in 'Specify skip rule' but with no luck

/task:task/task:payload/ns2:getAssignmentByTransactionIdResponse/ns2:result/ns6:Username='47236'

i want to know what is the wrong with this expression , does the syntax is wrong ?

Thanks a lot.