formula to determine first 2 characters

In the table, there are 5 field. ohjob1-5

I need to show them if they start with 'GR'

SO in the formula, I want to say.

If OHJOB1 starts with 'GR' then ohjob1? the truth is i believe they want the max.

the data would be something like this.

GROUP1, GROUP5, GROUP9

I want to show GROUP9 only if possible.  I have this formula called JOB1 to see if GR is there.

Left({OEORh2.Ohjob1},2) = 'GR'

this will return true or false. How to determine which has the largest group number?  I need something like this.

if job1 = true then {OEORH2.OHJOB1} for  showing the 'group' data. how to get the largest of the group' is a different issue.