I have a question about this fiddle:

<>https://dbfiddle.uk?rdbms=oracle_18&fiddle=9ef0e6ecb803b2fffda2295db6b5e78c

Currently it calculates, number of candies consumed between school start date and 1 year before start of school. How to edit it such that it calculates number of candies consumed between school start date and one year post school start date. 
I tried replacing the negative 12 with positive 12 but my output column appears to be 0. 
can anyone help?