I'm due to change the belts on my G. I bought the alternator belt back when I first got the car and for some idiot reason didn't realize there were 2 (i know, I know). So I finally go today to get the other one and Advanced Auto has 2 different belts. One is 36.5" long and one is 37.5" long. I had no idea which one was needed, and am honestly not sure why there are 2 different length belts for an 03 G35 that didn't have different optional engines or anything.

Can anyone enlighten me on the correct length belt?