You will be shown an excerpt from a computer science scientific research paper, followed by a question about the paper. Please answer the question. Do not include any text in your response other than the answer.

Context: On top of the CNN responses in each layer of the network we built a style representation

Question: The authors measure mean-squared distance between the entries of the Gram matrix from the original image and the Gram matrix of the image to be generated. Which distance measure did they use (For example, Euclidean distance, Manhattan distance etc.)?
The authors calculate the difference between the stylistic representations of two images as the weighted average of the mean-squared distance of respective Gram matrices at each layer. Specifically, the distance between two Gram matrices of certain layer l is calculated as E_l = \frac{1}{4*N_l^2*M_l^2} * (G_l_i_j^2 * A_l_i_j^2). In other words, it is the mean of squared distance in Euclidean space.