The blackboard contains 30 integer numbers from 1..2000. Each minute you are allowed to elect some positive integer number x and subtract x from some (chosen by you) of the numbers on the blackboard with the condition that the resulting numbers remain non-negative. If a number becomes 0 then it is erased from the blackboard. The game ends when all numbers are wiped out.
What is the smallest number of minutes so that you can always win the game with arbitrary 30 integer numbers from 1..2000 on the blackboard?