input: Write a python function that returns the smallest natural number whose factorial can be divided by x without a remainder.
  assert smallest_factorial_divisor(10) == 5
  assert smallest_factorial_divisor(15) == 5
  assert smallest_factorial_divisor(5) == 4
output: def smallest_factorial_divisor(x):
      def factorial(n):
          result = 1
          for i in range(2, n + 1):
              result *= i
          return result
  
      n = 1
      while True:
          if factorial(n) % x == 0:
              return n
          n += 1