So I have been in the US for the last 4 years on an F1 visa. Followed all the procedures and left the country before my F1 visa expired. However now I am trying to apply for a B1 visa to the US and while filling up the DS 160 form, it asks me to list the details of my previous US travel. Under this question, for length of visit, it only allows me to select a maximum of 180 days. Since I was on an F1 I was there in the country for a much longer time than 180 days. What's the best way to fill this section in?