Xiao Ming wants to use three small sticks to enclose a triangle. First, he chooses two sticks whose lengths are 5 cm and 8 cm respectively. How many centimeters is the stick.
小明要用三根小棒围三角形，先选了长度分别是5厘米和8厘米的两根，如果再从长度分别是3厘米、4厘米、13厘米的小棒中选一根，那么他应该选择长度是多少厘米的小棒．
<result>4</result>