Cumulative Sum SOS No VBA Expert

Hello to all,
I am writing to try to come to terms with a problem that I have difficulty solving.

I have a table of data where numeric values ​​are entered periodically in cell B3.
I expect that in cell C13 appears the sum of all the values ​​entered over time.
For example in B3 I insert from Monday to Friday 100, 200, 300, 400 and 500.
Daily in C 13 should appear 100, 300, 600, 1000 and 1500.

This operation is applied to several cells inside the same worksheet but for now I stick to a single to understand the underlying logic.

I tried to impose an iterated calculation to Excel with a single iteration. It works although I'm not sure or I do not have a robust system.
Does anyone have any suggestions that you can kindly share?
Many thanks in advance.

I posted it here, thinking that only a simple macro can make everything will work and also to make up for my shortcomings deadline of running this system....

Hello,
thanks for replying. I’ve triestino with SUM and SUM IF. However since the Numbers of input per sheet is prettamente high it is not easy to handle.
The goal is to insert i to the cell (i.e. B3) of a bell of materiale how many pieces of component A, after, with a second bill of material on the very same cell I modify A again, etc.
After each input, in another cell I should get the sum of the whole input of A I did.
Mano thanks

I tried this macro suggested to me:

Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False
If Not Intersect(Target, Cells(3, 2)) Is Nothing Then
Cells(13, 3) = Cells(13, 3) + Target
End If
Application.EnableEvents = True
End Sub

It works but now I have 2 questions:

1) The nymber to be added is the result of a multiplication not of a physical input. How to solve it?
2) How can I extend the macro to several cells on the same worksheet?

Thanks a lot!