auto weight calculating

hi, i have some weights(kg) in cell A2. so i have two type of packages to fill that weights.one package is 1.5kg & other one is 1 kg. i want use that two package to fill that A2 cell weights with less different. always first priority need to give to 1.5 kg, but there are two conditions.

01. always 0.5 kg need to add to A2 cell weights.
02. for weight adjusting u can use only maximum 2 of 1 kg packages.

so as a example to fill 13.8 kg result should like bellow..

=13.8+0.5 = 14.3

so i have to use 9 ,1.5 pks & 1, 1 kg pks. result will be - 14.5 ( that mean only different 0.2kg with actual requirement) if i use 10 of 1.5 kg, then result is =15 ,that mean i have used more than 0.7 kg. best option is first one.

13.8
1.5 kg -9
1 kg -1
pls check the sample sheet..
so i don't no this is can manage with excel formula or not. so pls help me. thanks a lot...