I am trying to figure out the best way to calculate a year to date total in a
particular spreadsheet. Here is an example of what it looks like

Number of months 4
1 2 3 4 5 6
a 100 100 100 100 100 100
b 100 100 100 100 100 100
c 100 100 100 100 100 100
d 100 100 100 100 100 100
e 100 100 100 100 100 100
f 100 100 100 100 100 100
g 100 100 100 100 100 100

So what I need to do is find a formula that will go across each row and only
up the cells that are equal or less than the number of months number that has
been put in. So say for instance I want four months of data then each row
should bring back a value of 400 (100 for 1, 100 for 2, etc...) Please tell
me this is possible, it seems like it should be very simple but I can't
figure it out!!! Thank you for any help you can offer!