# [Wolfram Language (Mathematica)], <s>27</s> 26 bytes

    #(10^IntegerLength@#-1)/9&

[Try it online!][TIO-l668io35]

[Wolfram Language (Mathematica)]: https://www.wolfram.com/wolframscript/
[TIO-l668io35]: https://tio.run/##y00syUjNTSzJTE78n6Zg@19Zw9AgzjOvJDU9tcgnNS@9JMNBWddQU99S7X9AUWZeSbSyrl1atHJsrJqCvoNCtaGOgqEREBsYgBjGOgpm5haWOgomFoamhmZGxiZGtf8B "Wolfram Language (Mathematica) – Try It Online"