f()(read a;date -d${a// /-} +%s)
t=y*10000+m*100+_-$(date -d@$[86400-`f`+`f`*2] +%Y%m%d)
`f`
while
read y m MoreSameLess
do
echo ${_:t<0?8:!t*4:4}
done