function sumInput() {

  let numbers = [];

  while (true) {

    let value = prompt("    .", 0);

    //   
    if (value === "" || value === null || !isFinite(value)) break;

    numbers.push(+value);
  }

  let sum = 0;
  for (let number of numbers) {
    sum += number;
  }
  return sum;
}

alert( sumInput() );