input: Write a python function that returns the n-th smart number.
  assert smartNumber(1) == 30
  assert smartNumber(50) == 273
  assert smartNumber(1000) == 2664
output: def smartNumber(n):
      def count_divisors(x):
          count = 0
          for i in range(1, int(x**0.5) + 1):
              if x % i == 0:
                  count += 1
                  if i != x // i:
                      count += 1
          return count
      
      count = 0
      num = 1
      while True:
          if count_divisors(num) == 4:
              count += 1
              if count == n:
                  return num
          num += 1