Bash, 66

LANG=C sed -r '/^-?(0|[1-9][0-9]*)$/q;s/.*/5000000/;q'</dev/random

It almost always prints 5000000. But if it found a valid number in /dev/random, it will print that number instead.

And this one is faster:

LANG=C sed -r '/^-?(0|[1-9][0-9]*)$/q;s/.*/5000000/;q'</dev/urandom