There are 6 sticks of unequal length, and these 6 sticks can be used to form an equilateral triangle with two sticks on each side. It is known that the lengths of 5 wooden sticks are 25, 29, 33, 37 and 41 centimeters respectively. How many possible lengths are there for the sixth stick?
有6根互不等长的木棒，用这6根木棒可以组成每边都有两根木棒的等边三角形．已知其中5根木棒的长度分别为25、29、33、37及41厘米．那么第6根木棒有多少种可能的长度．
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