code: def sanitize_cloud(cloud: str) -> str:
      
      if len(cloud) < 4:
          return cloud
      if not cloud[3].isdigit() and cloud[3] != '/':
          if cloud[3] == 'O':
              cloud = cloud[:3] + '0' + cloud[4:]  # Bad "O": FEWO03 -> FEW003
          else:  # Move modifiers to end: BKNC015 -> BKN015C
              cloud = cloud[:3] + cloud[4:] + cloud[3]
      return cloud
docs: Fix rare cloud layer issues