What would be the formula if possible for this setup I'm trying to use?

Cell A Cell B
2 67

When I input 2 in cell A, I want cell B to change to 69. I know how to do
that but the problem I'm running into is when I come back the following
month, and put lets say 6 in cell A, I want add 6 to the already 69 to make
75. So, another words almost like a running balance but within cell b.

So, another words, I want to add cell a to cell b to create a new total,
then take that new total the next month and add cell a to create a new total
but within cell b. Is this possible? Thank you.

TL