Using Custom Calculation Script box in Acrobat Pro X

I would like to simply subtract several fields from one field and have the result show up in final/total field when a user clicks her mouse in the field. I have used the custom calculation script. What is wrong with the code below? Without the <script></script> it doesn't work; with it, it  complains about a missing } at the end. I am an extreme novice with JavaScript, but it doesn't appear to me that I'm missing a }.

<script type="text/JavaScript">

function(){

event.value = this.getField("Total College Expense").value - this.getField("Less Prepaid Total").value - this.getField("Less Procurement Card").value - this.getField("Less Advances").value - this.getField("Amount Due: College").value;

}

</script>

Thanks for any help you can offer!

Kirsten