Trivially the largest digit is $9$, so lets delete to get as many $9$ in the beginning as possible: Delete $12345678$ so far $8$ digits $92$ to go... Delete $101112...17181$ so far $8+19$ digits $73$ to go... Delete $202122...27282$ so far $27+19$ digits $54$ to go... Delete $303132...37383$ so far $46+19$ digits $35$ to go... Delete $404142...47484$ so far $65+19$ digits $16$ to go... And then the fun starts, we have so far $99999505152535455565758...99100$ and $16$ digits to go: The biggest number in the $17$ digits after the $99999$ is $7$ so: Delete $505152535455565$ so far $84+15$ digits $1$ to go... $99999758...99100$ Delete $5$ $99999785960...99100$

9999999999

u delete 100 numbers that r not 9n's