Quick A: Write the type!

Recently on SO:

How to use auto keyword to assign a variable of type uint32_t or uint64_t in C++

I'm assuming you're working with the AAA style suggested by Herb Sutter.

In that case, a nice solution is to simply write:

auto variable_name = uint64_t{ 5000000000 };

This is clear, consistent, and explicitly typed with no nasty C-preprocessor necessary.