reference multiple sheets

[the6thplague]

hi,
I have an excel file with a lot of sheets in it. One sheet is named "main" and the other ones are named: 1, 2, 3, 4, 5, etc...

I want to put the following function in the "main" sheet:

=COUNTIF('1'!M2:M23,B1 & A2) + COUNTIF('2'!M2:M23,B1 & A2) + COUNTIF('3'!M2:M23,B1 & A2) + etc...

The question is, is there a way to somehow tell excel to run the function to sheets 1 to 31 without typing a very very long function like above?

Thanks a lot.
Eyal.