Statement

Each year the Christmas decorations are prepared earlier and earlier. This year is no exception, and William wants to be prepared! William is planning to put a really big Christmas tree in his garden, bigger and brighter than everyone else! The tree is built starting from a big pine tree, where many lights are installed on the branches. Starting from the root one or more cables are installed, and when there's a branch a light is placed there and one or more new cables come out of it. When a leaf is reached a new light is placed together with a switch. Pressing the switch will toggle all the lights in the path from that leaf to the root (turning on the switched off lights and vice-versa). After all this work William turns on all the N lights but realized that his tree is pretty boring. To avoid re-routing all the lights he decides to assign a niceness level A_i to all the N lights (A_i might be negative as well). If a light is turned off its niceness level goes to zero...