用VB编写程序：有一N个数的数列,知前3个数,从第4个数开始分别是它前3个数之和,计算并打印这个数列

Private Sub Command1_Click()
Dim i,n As Integer
Dim a() As Integer
n = Val(InputBox("序列的个数","",4))
If n < 4 Then End
ReDim a(1 To n)
a(1) = Val(InputBox("序列的第1个数","",0))
a(2) = Val(InputBox("序列的第2个数","",0))
a(3) = Val(InputBox("序列的第3个数","",0))
For i = 4 To n
a(i) = a(i - 1) + a(i - 2) + a(i - 3)
Next i
For i = 1 To n
Print a(i)
Next i
End Su