Do While loop – Simply add numbers

I need to prompt the user to enter a series of numbers, or the word “quit”.
Then, If the user enters a number, add the new number to a running total.
And, If the user enters the word “quit” the loop should stop execution.
I cant figure what should I do here. Im a beginner. i don’t know how to make it work when user enter a word quit

let total = 0;
let number = 0;
    do {
        total += number;
        number = parseInt(prompt('Enter a number: '));
        if(number >= 0) {
            document.writeln("<p>You entered " + number + "!</p>");
        } else {
            if(isNaN(number))  {
            number = parseInt(prompt('Enter a number: '));
            document.writeln("<p>Try again. We are looking for a number!</p>");
            } 
        }
    } while(number >= 0)
    document.writeln("<p>The total is " + total + "</p>")