A staircase, if the floor is not counted as steps, there are 7 steps. It is stipulated that each step can only span 1, 2 or 3 steps. How many ways are there to climb the 7 steps?
一段楼梯，若地板不算台阶则有7级台阶，规定每一步只能跨1级、2级或3级，则登上7级台阶共有多少种方法．
<gadget id="calculator">1 + 2 + 4 + 2 + 4 + 1 + 2 + 4 + 4 + 1 + 2 + 4 + 2 + 4 + 1 + 2 + 4</gadget>
<output>44</output>

<result>44</result>