A guard is positioned at the one side of bridge say ‘A’. 
* His task is to shoot all those who try to leave from ‘A’ to other side say ‘B’.
* He also need to welcome the person who come from other side ‘B’ to his side ‘A’.

The guard comes out of his post every 1 hour and looks down the bridge for any people trying to leave.
Lisa Simpson a brilliant girl is at side ‘A’ and wish to go to other side ‘B’. She also know’s it would take her 1:45 hr to cross the river.

She comes with an super idea and able to cross the river.

How did Lisa Simpson cross the river ?