Determine the GCD of 1000000000 and 1000 000, 005.
$$
\begin{aligned}
P G C D(1000000000,1000000005) & =P G C D(1000000005,1000000005-1000000000) \\
& =P G C D(1000000005,5) \\
& =5
\end{aligned}
$$

since $5 \mid 1000005$.