Multiselect - if condidion to.String

Hi,
I have a Multiselect field in which, in On user input, I put:

if (input.Setor.toString() != "-Select-")
{
    if (input.Setor == "Assistência")
    {
        hide Number1;
        hide Number2;
        hide Number3;
        hide Number4;
....
System return that:
Error in statement at line number 3
The Left expression is of type STRINGLIST and the right expression is of type STRING and the operator == is not valid here
I try to quit toString or put toLong, but nothing.
Any help?
Thanks

Mic