# [Neim], 7 bytes

    'π𝐂𝕋𝐬S𝕊

Explanation:

    'π         Push 345
               The character ' pushes the next character's index in the codepage plus 100.
               The characters ", + and * do that same thing except add a different number.
               This means that in Neim, all 3 digit numbers can be expressed with 2 characters.
               This commit was pushed 8 days before the answer was posted.
      𝐂        Get the characters
       𝕋       Vectorised multiply with the input
        𝐬       Sum the resulting list
         S𝕊    Subtract the input

Alternative program: `3𝐈ᛖ𝕋𝐬S𝕊`

Instead of pushing `345` and then getting the characters, creates the array `[1 2 3]` using `3𝐈`, then adds 2 to each element with `ᛖ`.

[Try it online!][TIO-j4r3x911]

[Neim]: https://github.com/okx-code/Neim
[TIO-j4r3x911]: https://tio.run/##y0vNzP3/X/18w4e5E5o@zJ3aDaTXBAMZXf//RxsqGCkYx3IZAwA "Neim – Try It Online"