input: Write a python function to find the length of the longest increasing subsequence.
  assert LIS([10, 22, 9, 33, 21, 50, 41, 60]) == 5
  assert LIS([3, 10, 2, 1, 20]) == 3
  assert LIS([3, 2]) == 1
  assert LIS([50, 3, 10, 7, 40, 80]) == 4
output: def LIS(arr):
      if not arr:
          return 0
      
      n = len(arr)
      lis = [1] * n
      
      for i in range(1, n):
          for j in range(i):
              if arr[i] > arr[j] and lis[i] < lis[j] + 1:
                  lis[i] = lis[j] + 1
      
      return max(lis)