how to get randomly generated numbers to equal a set value?

Here is the question at hand

so in short, I need to randomly generate 6 numbers between 1-1000, and the 6 numbers added together must equal 1000

here's what I have so far

    public static void main(String[] args){
    Scanner keybd= new Scanner(System.in);
        System.out.println("In 1000 rolls of dice, I got: ");
        int sum = 0;        

        for(int side=1; side<= 6; side++){
        int number = (int)(Math.random() * 1000 + 1);       
        System.out.println(side + "‘s " + (number);
        sum = sum + number;
                }   
             }
    }

All it does is just print out 6 random numbers between 1-1000

I just can't figure out how to make it so that the numbers added together equal 1000

Any help will be appreciated!