This is a solution for the Project Euler Problem 5:
http://projecteuler.net/index.php?section=problems&id=5

Just compile all source files with e.g.:
gcc *.c *.h

Then run it with:
./a.out

Enter any number and you get the result.
Though be careful: The calculation for 25000 lasts 1 minute ...

Just to prevent questions: I did this in C to improve my skills in that language.
I know, in most other languages (for example python) it would be loads easier and
the code would be shorter and it even would support arbitrarily high numbers, yadda yadda ^^.