Shellscript Sample: Sum up input numbers

This shellscript sum up the numbers from arg1 to arg2.

#!/bin/sh

i=0
sum=0
if [ $# -eq 0 ]; then
    echo "No input parameter!"
elif [ $# -eq 1 ]; then
    echo "Plese input 2 parameters!"
else
    i=$1
    for i in seq $1 $2; do
 sum=`expr $sum + $i`
    done
    echo "$1 + ... + $2 = $sum" 
fi

exit 0