excel formuala

I need a spreadsheet column that has the following formula. If I choose a number for a total such as 3000 for example. I want all of the numbers in the column above this to always equal 3000 If I change the first number to 50 then all of the rest of the nunbers will total to 3000 and this goes on until I reach the very last number in the column. I may have 40 numbers in the column but I want the sum of the all of the numbers to always equal the total value I enter.