I have a spreadsheet with values like so:

```
blah 1 12
2 12
3 12
foo 1 6
bar 1 2
foo 1 6
2 5
```

Numbers in the middle column range from 1 to 8; numbers in the right column range from 1 to 12. The middle column is always in order with no gaps, but can reset back to 1 after any value. The left column always has a nonblank (but not necessarily unique) value on a 1 row and a blank value on a >1 row. The values for the >1 rows are *usually* the same as the 1 row, but not always (and I don't want to assume they are).

I would like to add a new column with a single formula that, for each row:

- if the first number is a 1, then sum all of the second numbers up to but not including the next row with a 1.
- if the first number is anything else, then output 0.

ie. the required output for the data above is:

```
36
0
0
6
2
11
0
```

If it's easier, the sum could appear on the highest-numbered row of each subgroup instead of the 1 row (though I definitely prefer it on the 1 row). But the row relationships have to be maintained -- it can't output only 4 rows.

Alternatively, the grouping decision could be based on the blank/nonblank column instead of the counting column; again, if that's easier.