How many six-digit odd numbers are possible if the leftmost digit cannot be zero?

Right, so that means starting from 100000 and ending at 999999
how many numbers is that?
999999-100000=899999

but how many of them are odd?
let's take a smaller sample
start with an even and end with odd
from 2 to 7
that is 5 number difference, but the odd numbers are 3 and 5 and 7, so 3 of them
so it seems that for a n number difference when start with even and end with odd, you have (n+1)/2 odd numbers

so
899999 number differnce
(899999+1)/2=900000/2=450000 odd numbers