convert ssh key from putty (ppk) to openssh

Recently I've had to migrate an SSH key generated on a Windows 10 machine to a Debian workstation. You'll just need two commands, probably:

sudo apt install putty-tools
puttygen your-windows-10-private-key.ppk -O private-openssh -o your-openssh-private-key-name

And that's it! This will get your private key on a format that openssh will recognize.
To check your public key just run:

puttygen your-windows-10-public-key -L

Put it wherever you like!