Statement

Christmas is coming and, as you may easily imagine, this is the most stressful period of the year for Santa Claus. One of his resolutions for this year is to organize better the delivery of the gifts. He has instructed his assistants to take a map of the city and divide it in N × M rectangular neighborhoods. For each, they have also reported the total number of gifts which should be delivered. Santa's headquarter, which is the starting point, is located in the neighborhood (x,y) in the map. From there, the van is able to reach an adjacent neighborhood (in the four directions) in a minute. Santa's benevolence and generosity are not in his favour: when he crosses with his van a neighborhood, even if he has already delivered the gifts, children demand again the same gifts. Santa Claus, who is pure-hearted, is unable to refuse and gives them another load of gifts...