How to rewrite an nested IFF statement to oracle case when statement

How to rewrite the following nested IFF statement to oracle Case when statement .

IIF(IN_RNK = 1,
IIF(IN_SUM > 2,IIF(IN_MTR_COVERAGE_NUMBER_A = 'A','ORIGINAL BASE','ORIGINAL RIDER'),IN_MTR_COVERAGE_NUMBER_A),
IN_MTR_COVERAGE_NUMBER_A)

>Solution :

Like this:

CASE
WHEN IN_RNK = 1
THEN CASE
     WHEN IN_SUM > 2
     THEN CASE 
          WHEN IN_MTR_COVERAGE_NUMBER_A = 'A'
          THEN 'ORIGINAL BASE'
          ELSE 'ORIGINAL RIDER'
          END
     ELSE IN_MTR_COVERAGE_NUMBER_A
     END
ELSE IN_MTR_COVERAGE_NUMBER_A
END

Which can be simplified to:

CASE
WHEN in_rnk = 1 AND in_sum > 2 AND in_mtr_coverage_number_a = 'A'
THEN 'ORIGINAL BASE'
WHEN in_rnk = 1 AND in_sum > 2
THEN 'ORIGINAL RIDER'
ELSE in_mtr_coverage_number_a
END