How to perform an order logic in SSIS package for inserting value from source to destination by an oder of column being not null

How to perform an order logic in SSIS package for inserting value from
source to destination by an oder of column being not null

I have 4 columns in source table.
Source Table : Column 1, Column 2, Column 3, Column 4
Among those 4 columns from source table, I want to insert only 2 columns
in the destination table.
Destination table : has column A and Column B
To insert value in Column A and Column B. Now i want to perform order
operation in SSIS package.
So I want to have an oder logic in SSIS .
If there is a value in Column 1, then use that in Destination Column A and
insert from column 1 value into Column A . So, if there is value in Column
1, then Column A in destination table will be inserted.
IF there is no value in Column 1, then check the Column 2 in the source
table and if there is value in Column 2, insert that value in Column A.
Now suppose, Column 1 was null and Column 2 had value, Column 2 value will
be inserted into column A in the destination table.
Now check the column 3 in source and see if there is value, if it has
value then insert that value in Column B in Destination table. If there is
no value in Column 3 then check column 4 from source.
So basically check in those 4 columns in the order (which is specified)
and 1st value that we come across, use that in the destination Column A
and Column B.
There is tricky part is there, so 1st not null value goes into the
Destination column A and 2nd not null value goes into 2nd destination
column B, how can i figure it out which one is 2nd not null value?
I guess we can do this in SQL but I want to do in SSIS package.
I will really appreciate your help. Thank you in advance.