Pivot Table Running Total Year and Month

[Nos03]

I'm trying to get the running total from 2010-2012. I would like to have this done inside of a pivot table. I'm having an issue where the running total is only working for each year. The final number for 2010 is 10.9, then for January 2011 its 2.4. Is there any work around so that the year doesn't reset the running total? Thank you in advance.

2010
May	0.1
June	1.2
July	2.4
August	3.4
September	4.4
October	5.9
November	8.0
December	10.9
2011
January	2.4
February	7.2
March	10.6
April	38.3
May	49.2
June	53.0
July	60.4
August	96.8
September	100.2
October	105.3
November	109.4
December	111.1
2012
January	12.0
February	17.6
March	22.4
April	83.9
May	89.1
June	89.5

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