In serbia all males.

In Russia the 10% must serve in the army. But that was introduced recently.
But you must calculate the number of people that served the army before the reforms. People above 25 years.
As you could have seen, the Russian army is reforming to be professional. Made out of contract soldiers and volunteers.

So the capacity of Russian army is much bigger than 4 million. But in the coming years it will drop, as les young people serve the army.