5 Fibonacci Sequence

echo Enter the fibboncci term
read N
i=3
if [ $N -eq 1 ]
then
    current=0
elif [ $N -eq 2 ]
then
    current=1
fi

below_prev=0
prev=1
current=0

while [ $i -le $N ]
do
    current=`expr $below_prev + $prev`
    below_prev=$prev
    prev=$current
    i=`expr $i + 1`
done
echo $N th term of sequence is $current