Max value of a subset of elements over a field

Hi guys i have this problem: on the above table i have to calculate a field 'Init Time'. This field has to be calculated as the following:

• the transitions from state A to state B could be only: 30->40; 40->51; 51-> 61 or 51->71; 61->51.  the state 51 and 61 can form a loop.
• The init state as to be the max value of the 'status B time' that is minor of the actual 'status B time' . For example:  on the second row, the init time as to be 2 because the previous state is only 40 and there is only one 40 state with time 2. On the sixth row, instead the init time has to be 10 because it is the max time among (2,8,12 )  that are the time of the states that could be previous of 51 (1 state 40 and 2 states 61).

Below there is an example of the resulting table.

Thank you for any suggestion