func checkPerfectNumber(num int) bool {
	if num <= 1 {
		return false
	}
	sum, sqrt := 1, int(math.Sqrt(float64(num)))
	if sqrt*sqrt == num {
		sum += sqrt
		sqrt--
	}
	for i := 2; i <= sqrt; i++ {
		if num%i == 0 {
			sum += i
			sum += num / i
		}
	}
	return sum == num
}