Fetching part of email subject to set a variable

Fetching part of email subject to set a variable

When using "Set Variable" in Flow, is it possible to insert a formula in the value field, something like:
${fetchEmail_1.subject}.substring(20.29);

or maybe:
mid(${fetchEmail_1.subject}, 20, 29);

I'm trying to extract part of the email subject line (numeric) to use in further automation.