//https://projecteuler.net/problem=1

​

//sum of multiples of 5 (<1000), using formula for arithmetic series

let sum = (5 + 995) / 2 * 199;

​

//sum multiples of 3 (<1000) that are not multiples of 5

let n = 3;

while (n < 1000) {

  if (n % 5 !== 0) {

      sum += n;

  }

  n += 3;

}

​

console.log(sum);

//Note: Answer is reasonable since 1 + 2 + 3 + ... = 500500.