Using relative positions in Excel formulas

How do I create a formula that isn't made invalid when I delete a row.

For example in cell F12 I have the formula: =F11+D12-E12

This basically says take the value from the cell above then add the value of the cell 2 to the left and subtract the value in the cell directly to the left.

However, because I'm using actual cell addresses, as soon as I delete a row, all the rows below become invalid.

How do i express the formula by relative position (ie = "1 above" + "2 to left" - "1 to left")

Thanks.