input: Write a python function to find the least common multiple (LCM) of two numbers.
  assert LCM(15, 20) == 60
  assert LCM(3, 5) == 15
  assert LCM(7, 9) == 63
output: def LCM(a, b):
      def gcd(x, y):
          while y:
              x, y = y, x % y
          return x
      
      return abs(a * b) // gcd(a, b)