Select one number between others with spaces

Select one number between others with spaces

Can I select the number 3433 in this example of generated file with so
many spaces that I can not control?
BIOLOGIQUES
3433 130906 / 3842
Please see the example here : http://regexr.com?368ku
The number 3343 could change from one file to an other, but it will have
always the same position/
I'm using regex with php.
It's a pdf document that I transform with pdftotext function of xpdf and
so I must have that number which change from a pdf to an other.
It's very bad positioned and I don't know how to capture it via regex.
I tried:
BIOLOGIQUES [^0-9]*\K([0-9]*)(.*)
http://regexr.com?368ku but it takes all the numbers, I need only the
first one.