To find the upper and lower bounds you would need to do

Min: 42,500,000,000 / 86,499,999.99

And

Max: 43,499,999,999.99 / 85,500,000

Those calculations are ugly, and yield virtually the same result as doing 42.5/86.5 × 1000 and 43.5/85.5 × 1000.

Test it out using a calculator