Dear StataList-ers!

Help! I need somebody! My question is very basic.

Panel data (countries, years). I have a variable, which equals the number of reported victims of human trafficking in each country in year t.
I am trying to generate a new variable, which would equal the average number of victims in country i for years t and t-1. I mean, "victims" in t-1 an in t = the average of "number of victims" in t-1 and in t.

I tried
Code:
 sort country_coded year
bysort country_coded:gen victims =(Numberofvictimsoftrafficking[_n-1] + Numberofvictimsoftrafficking[_n])/2
Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input long country_coded int(year Numberofvictimsoftrafficking) float victims2
1 2008 108    .
1 2009  94  101
1 2010  97 95.5
1 2011  84 90.5
1 2012  92   88
1 2013  95 93.5
2 2003  45    .
2 2004  35   40
2 2005  37   36
2 2006  38 37.5
end
label values country_coded country_coded
label def country_coded 1 "Albania", modify
label def country_coded 2 "Austria", modify
Obviously, I am wrong. Please, help to sort it out!

Thanks in advance