Convert date from current month to first day of prior month

I am trying to convert a date to the first day of the previous month. For example, in cell AY the value is 10/31/2010. The formula in cell AX2 is:

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The resulting value from formula is 10/1/2010. I want it to convert to 9/1/2010. Thanks in advance for any comments.

In summary:
10/1/2010 converts to 9/1/2010
10/5/2010 converts to 9/1/2010
10/30/2010 converts to 9/1/2010
....and so on

Try:

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Cheers,

Or =EOMONTH(A1,-2)+1

Try

=AY2-DAY(AY2)-DAY(AY2-DAY(AY2))+1