input: Write a python function to determine the smallest natural number whose factorial can be evenly divided by x.
  assert smallest_factorial_divisible_by(10) == 5
  assert smallest_factorial_divisible_by(15) == 5
  assert smallest_factorial_divisible_by(5) == 4
output: def smallest_factorial_divisible_by(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