Count Column A only up to last nonblank cell in Column B

I need to count the number of days in column A with the condition of last nonblank cell in Column B. In the ex. below the answer should return 18.



Column A Column B
7/1/2011
7/2/2011 0.70612
7/3/2011
7/4/2011 0.6942
7/5/2011
7/6/2011 0.70612
7/7/2011
7/8/2011
7/9/2011
7/10/2011 0.70142
7/11/2011
7/12/2011
7/13/2011
7/14/2011
7/15/2011
7/16/2011
7/17/2011
7/18/2011 0.6956
7/19/2011
7/20/2011
7/21/2011
7/22/2011
7/23/2011
7/24/2011
7/25/2011
7/26/2011
7/27/2011
7/28/2011
7/29/2011
7/30/2011
7/31/2011

Assuming each cell always steps by 1 day:

=MATCH(9.99E+307,B1:B31)-ROW(B1)+1

Yes, thanks Azam and zbor. Both nailed it. I guess, I'll use zbor's because my excel IQ is low. Don't know what indirect combined in a range indicate.
@Colin Legg formula returns 1 cell short. What's with 9.99E+307?

Many, many thanks guys.

What's with 9.99E+307?

9.99E307, 99^99, 9.99999999999999e+307 -- these are all just very large numbers - larger than any value you're going to have in column B.

@Colin Legg formula returns 1 cell short

It returns 18 for me.

How about -Row(B1)?

That's a reference to the first cell in the range. So if your range is B6:B36 then you'd use -ROW(B6). But, I think Zbor's formula will suit your needs better (it subtracts the first date from the last date thus giving a date difference in days, as opposed to counting the number of rows)?