Averageif with in average if

I have a data set that has Material (Col A) Plant (Col B) Storage Loc (col C), and Safety Stock (col D). The safety stock will be the same for every row with the same material plant combo even thought the Storage loc may change. I need to look up the total safety stock for each material. So i need a formula that will do a Sum if of the material but with a function inside it to average or find the unique values only at the material/plant level.