How can I change a cell daily

Hello,

I will try to explain the best I can,

I have some cells 'A1, A2, A3, A4' that I fill up daily with numbers

ex:
-day1 I will input in 'A1',100$
-day2 I will input in 'A2', 94$
-day3 I will input in 'A3', 98$
-day4 I will input in 'A4', 96$

Now I have 3 more cells:
- 'B1=A1-A2'
- 'B2=A1-A3'
- 'B3=A1-A4'

And here comes the question:

I have cell 'C1' that needs to be B1 in day 2, then B2 in day 3 and B3 in day 4.

Ex:
C1 for day1=0$, day2=6$, day3=2$ and day4=4$

Hope I am not asking for too much.

Thank you in advance for your help