过程调用问题，不知道怎么运行，求解劝
5．运行以下程序，输出的结果为__________。Private Function fact(n As Integer) As Integer
fact = 1
Do While n > 0
fact = fact * n
n = n - 1
Loop
End Function
Private Sub Form_Click()
Dim sum As Integer, i As Integer
For i = 4 To 1 Step -1
sum = sum + fact(i)
Next
Print "Sum="; sum
End Sub
请高手给讲解一下，这个程序怎么运行，看了半天实在看不懂，谢谢
