function microbuzz(n) {
  var next_mult_3 = 0,
    next_mult_5 = 0,
    next_n = 0,
    answer = 0;

  while (next_n <= n) {
    if (next_n == next_mult_3 || next_n == next_mult_5) answer = answer + 1;
    if (next_n == next_mult_3) next_mult_3 = next_mult_3 + 3;
    if (next_n == next_mult_5) next_mult_5 = next_mult_5 + 5;
    next_n = next_n + 1;
  }

  return answer;
}

console.log(microbuzz(10000));