a = 1 * 2 * 3 * ... * 2018
b = 1 + 2 + 3 + ... + 2018
b=2018*2019/2
b=1009*2019
b=1009*(2018+1)
b=1009*2018+1009
a+b=1 * 2 * 3 * ... * 2018+1009*2018+1009
a+b=2018*(1 * 2 * 3 * ... *2017 +1009) +1009
(a+b):2018=1 * 2 * 3 * ... * 2017 +1009 rest 1009
a) restul=1009