JIRA Structure formula

[Abhinav Singhal]

we have 8 priority-style labels (A-1 = highest, H-8 = lowest) or (H-8, G-7, F-6, E-5, D-4, C-3, B-2, A-1 )tagged with JIRA issues 
If an issue has multiple labels, we want Structure formula to compare them and display the **highest-priority one (A-1 > … > H-8)*.

• If an issue has ["C-3", "F-6"] → formula returns 3 (C-3).

• If it has ["B-2", "E-5", "H-8"] → formula returns 2 (B-2).

I am loading all issues in JIRA structure and created below formula 

WITH priorityOrder = {
"A-1": 1,
"B-2": 2,
"C-3": 3,
"D-4": 4,
"E-5": 5,
"F-6": 6,
"G-7": 7,
"H-8": 8
};

WITH best = MIN(FOR l IN LABELS: priorityOrder[l]);
FIRST(FOR l IN LABELS: IF priorityOrder[l] = best: l)

it is not working do we have any solution for the same