Does anyone have any suggestions on how to use indirect function for my case?

There is a list of numbers under column A, and there is a input value in
cell B1
On column C, I would like to sum up the numbers on upside and downside.
For example,
In column A, and the input value in cell B1 is 4, then in cell C9, I should
sum up all values between [A5] and [A13], for cell C9 = 4+1+8+4+5+6+0+9+8 =
37
[A1] 5
[A2] 8
[A3] 9
[A4] 3
[A5] 4
[A6] 1
[A7] 8
[A8] 4
[A9] 5
[A10] 6
[A11] 0
[A12] 9
[A13] 8
[A14] 3
[A15] 2
[A16] 5
[A17] 7

Using this approach, I would like to determine the rest of number under
column C.
For exception, in cell A4, there is no 4 addition rows on upside, so it
should return "". In cell A15, there is no 4 addition rows on downside, so
it should return "".
N.B. The number of row to sum up on upside and downside is a variable based
on the input value in cell B1.

This coding is too complicated to me, can anyone please help for any
suggestions?
Thank in advance for any suggestions
Eric