已知A、B、C三点不共线，若点M与A、B、C四点共面，对平面ABC外一点O，给出下列表达式：$\overrightarrow{OM}$=x$\overrightarrow{OA}$+y$\overrightarrow{OB}$+$\frac{1}{3}$$\overrightarrow{OC}$，其中x，y是实数，则x+y=　____ 

    The polar bear is a very big white bear. We call it the polar bear because it lives in the Arctic Circle（北极圈） near the North Pole.

    The polar bear lives in snow and ice. At the North Pole there is only snow, ice and water. There is not any land. The polar bear has a very warm coat because the weather is cold in Arctic Circle. You can't find the polar bear easily in the snow because its coat is white.

    A grown-up polar bear is usually about three meters long and weights about 450 kilos. It can stand up on its back legs because it has very wide feet. It can use its front legs like arms. The polar bear can swim very well. It catches fish and sea animals for food. It goes into the sea when it is afraid. People kill the polar bear for its beautiful white coat. The governments of Canada and United States call on that people should stop killing polar bears. They don't want these beautiful animals to die out.

根据短文内容回答问题。

   There is a new park near Andy’s home. It’s fine today. Andy and his family are in the park now. On their left, there is a café. On their right, there is a big lake. There are many flowers and trees around the lake. There’s a small hill behind the lake. Near the lake, there are two signs. One says, “Don’t swim in the lake!” The other says, “No fishing!” But you can go boating on the lake. There is a beautiful garden in the middle of the park. There are green grass and beautiful flowers in it. There are some small shops between the lake and the garden. The park is so nice. Andy and his family like it very much.