I need a formula to count the number of times a semi-colon appears in a variable. This is actually for visual flow but it is a formula like any other in Salesforce.

Any ideas? I need the count not just a TRUE or FALSE result. 

My overall goal is I need to compare the values captured from a  multi-select picklist and identify if values were either added or removed from the list. So I plan on counting the number of ; and then using a decision module to take appropriate action on another object. 

Here is an example:

09:00:25:612 FLOW_VALUE_ASSIGNMENT 3327be5ac80f0d842d9d2f061289153095dc09d-1678|varTMPriorValues|BM Web Enroll;We Care

So I need to get back 1 from this variable. 
 

09:00:25:612 FLOW_VALUE_ASSIGNMENT 3327be5ac80f0d842d9d2f061289153095dc09d-1678|varTMValues|Aflac;BM Web Enroll;We Care

And I should get 2 back from this variable. 

So I can do my decision and know that values were added to the list.