def L1(yhat, y):
    """
    Arguments:
    yhat -- vector of size m (predicted labels)
    y -- vector of size m (true labels)
    Returns:
    loss -- the value of the L1 loss function defined above
    """
    ### START CODE HERE ### (≈ 1 line of code)
    loss = sum(abs(yhat - y))
    ### END CODE HERE ###
    return loss