The parcel section of the head post office is in a mess. the parcels that need to be loaded to the vans have been lined up in a row in an arbitrary order of weights. the head post master wants them to be sorted in the increasing order of the weights of the parcels, with one exception. he wants the heaviest (and presumably the most valuable) parcel kept nearest his office. you and your friend try to sort these boxes and you decide to sort them by interchanging two boxes at a time. such an interchange needs effort equals to the product of the weights of the two boxes. the objective is to reposition the boxes as required with minimum effort.