There are two wooden sticks, which are 20cm and 30cm respectively. If the length of the wooden sticks does not change, they must be nailed into a triangle. How many cm sticks should be selected as follows.
有两根木棒，它们分别是20cm和30cm，若不改变木棒的长度，要钉成一个三角形，应选取下列多少cm木棒．
<result>20</result>