[Solved] Using if function with #N/A Result from Index function

I have a spreadsheet in which I am trying to find the difference of two sets of values. To create the two value sets, I am using an index/match formula, which properly returns the error #N/A if there is no value to return.

In a scenario where this happens, I would like to be able to treat the #N/A as a 0. My thought was to do so using an if function, but I cannot seem to figure it out.

How would I write a formula to treat #N/A as 0?

Edit: Today I learned the IfError function exists. Thanks everyone.