len=''
i=0
sum=0
while read num; do
    if [ -z "${len}" ]; then
       len=$num
       continue
    fi
    (( sum += num ))

    (( i++ ))
   if [ ${i} -eq $len ]; then
       break
   fi
done
printf "%.3f" $( echo "scale=3; ${sum} / ${len}" | bc )