Excuse me , you are right, i changed my mind regarding what i want

NOW

i want the A1 cell to be updated every time a value in the cells of the column B,D,F is updated,

first i assign the starting value that we will subtract from it and in this case will be 1500,

then we start with b2 have 10 and d2 have 20 and f2 have 5

i want excel when the value in b2 inserted it subtracted from the 1500 and enter the result to A1 "1490" then when d2 value inserted 20 it subtract it from the A1 value "1490-20" > "1470 in A1"

so A1 now have 1470, next once the f2 value updated 5 the excel subtract that from the new A1 value "1470-5" and update the A1 with the result 1465.

I hope the idea is clear now