Edit in JSFiddle

//If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

function naturalNumbers(x) {
  return x
}

console.log('sum of all the multiples of 3 or 5 below 10:' + naturalNumbers(10)) // 23
console.log('sum of all the multiples of 3 or 5 below 100:' + naturalNumbers(100)) // MUST CREATE THE ANSWER
console.log('sum of all the multiples of 3 or 5 below 1000:' + naturalNumbers(1000)) // MUST CREATE THE ANSWER
console.log('sum of all the multiples of 3 or 5 below 10000:' + naturalNumbers(10000)) // MUST CREATE THE ANSWER