append a 0 at LSB and start scanning from LSB to MSB
if 1 is encountered after a 0 [ 10] then place -1 as shown in fig.
if 0 is encountered after a 1 [ 01] then place +1
if 0 is encountered after a 0 [ 00] then place 0
if 1 is encountered after a 1 [ 11] then place 0
then calculate no. of +1 and -1 's which is total no. of addition/subtraction operation required.
https://gateoverflow.in/3753/gate2005-it_8