copying dates based on sum of units

Hello experts,

I am trying to solve below problem. Wondering if macro or a formula can help.

Column A is the shipping date, Col B is the receiver ID, col C is the number of units shipped.

Now if the number of units on a day is 4 or more then the date entered in result column must be same as in col A within the same row.

If the number of units is less than 4 than check units in next row(date). if sum becomes 4 or more then enter the date corresponding to the row in the previous row.
So until the sum of units becomes 4 or more keep checking next rows and then enter max date for those rows.
Once the sum is 4 or more units go to the next row and check.

max 4 rows will need to be looked because within 4 rows the sum should come to 4.

Thanks