when we fire ls -lrt command we see o/p as

 
total 16
drwx------   9 root     root        8192 May  8  2002 lost+found
drwxr-xr-x   2 root     root         512 Jun 14  2002 TT_DB
drwxrwxr-x   2 root      root      512 Jul 31  2002 mail

This is from the Linux info pages:

Try the -s option and sum up the first column...

thanks a lot guys, got it that it is total no. of blocks the files occupy in that directory , i thought them to be no. of files or something used below code to find the total no. of bytes

sum=0 ; 
b=1;
n=`ls -lsrt |  awk -F " " '{print $1}' | wc -l`
n=$(($n-$b));
echo $n;
ls -lsrt |  awk -F " " '{print $1}' | tail -$n | while read x
 do sum=$(($sum+$x))
 done;
 echo $sum;

Not sure I understand what you want to achieve.
The sum you output is the total sum of blocks that ls outputs anyhow. This could be done with a oneliner as well:

$ ls -s1|awk 'NR==1{next} {sum+=$1} END {print sum}'