def amicable_numbers_sum(limit):  
    if not isinstance(limit, int):  
        return "Input is not an integer!"  
  
    if limit < 1:  
        return "Input must be bigger than 0!"  
  
    amicables = set()  
  
    for num in range(2, limit+1):  
        if num in amicables:  
            continue  
  
        sum_fact = sum([fact for fact in range(1, num) if num % fact == 0])  
        sum_fact2 = sum([fact for fact in range(1, sum_fact) if sum_fact % fact == 0])  
        if num == sum_fact2 and num != sum_fact:  
            amicables.add(num)  
            amicables.add(sum_fact2)  
  
    return sum(amicables)  
  
  
print(amicable_numbers_sum(9999))  
print(amicable_numbers_sum(999))  
print(amicable_numbers_sum(99))