Populate one field with one value from choice of four other fields

Hi, I have all but one item on a form working.  Under Calculation of Final Fee there are four different starting points, which self populates depending on what values the user enters in the earlier contract sum and change order fields. How do I populate a fifth field, the Calculated Fee near the bottom of the form, with whichever of the four possible totals shows up under Calculation of Final Fee? My script which isn't working is:

var v1 = this.getField("1Kto50KTotal").value;

var v2 = this.getField("50Kto100Ktotal").value;

var v3 = this.getField("100Kto500Ktotal").value;

var v4 = this.getField("500001andUpTotal").value;

if (v1 !==0) {event.value = v1} else if (v2 !==0) {event.value = v2} else if (v3 !==0) {event.value = v3} else if (v4 !==0) {event.value = v4} else {event.value = ""}

The form looks like: