def construct_ladder(pieces:list[int]):
     ladders = 0

     while len(pieces) > 0:
          currPiece = pieces[0]
          pieces.remove(currPiece)
         
          for piece in pieces:
               if currPiece + piece == 10:
                    ladders += 1
                    pieces.remove(piece)
                    break
     return ladders

# print(construct_ladder([1,9,9,1,9,6,6]))