How do I write a fast formula so the Original Hire Date always calculates to the earliest hire date?

Summary:

How do I write a fast formula so the Original Hire Date always calculate to the earliest hire date for the Employee work relationship?

Need a fast formula for the following requirements:

The Original Hire Date should always calculate to the earliest hire date for the Employee work relationship.

It should not adjust or recalculate when the employee leaves the organization and is rehired.

It should also retain any manual adjustments made by an end user.

Content (please ensure you mask any confidential information):

The Calculate Seniority Dates process will run daily to recalculate seniority dates based on data changes and the fast formula rule.