How to add values from the previous cell in the same column?

I have a column called total and I would like to create a new column in a repeating group called total1, the first column would have the values 10, 20, 30, 50 so the second column should add the cell’s previous value to the current one, so it should have the values 10, 30, 50, 80

Example

Total Total1
10 10
20 30
30 50
50 80