Google Sheets (Formula) - If one cell equals some value, it will return another value to a neighboring cell

I am trying to find a formula for the following in Google Sheets:

• If a cell (C4) has the value Mon, Tue, Wed, Thu, Fri, Sat, Sun. I want it to return a number to a neighboring cell (B4) - the number 1 for Mon, 2 for Tue, 3 for Wed, etc.
• I have scoured the internet for this formula and have found nothing. Those who assist, your help is greatly appreciated.