GROUPING BY DATETIME IN SAS DATA STEP

My data is in below form

account_no  transaction_start_dt_tm       RECTYPE   
34842765    23APR2017:14:34:00.000000        ICU      
34842765    25APR2017:17:26:00.000000        ICU      
34842765    28APR2017:14:18:00.000000        LLOC     

I want to enumerate rectype within the group that includes both account_no AND transaction_start_dt_tm. Account_no is constant, but transaction_start_dt_tm never repeats and Rectype has values of (ICU, LLOC). I want my output to be as shown below.

account_no  transaction_start_dt_tm       RECTYPE   RECNO_1 CNT
34842765    23APR2017:14:34:00.000000        ICU       1    1
34842765    25APR2017:17:26:00.000000        ICU       2    2
34842765    28APR2017:14:18:00.000000        LLOC      3    1