ValueError: Using a target size (torch.Size([16])) that is different to the input size (torch.Size([13456, 1])) is deprecated. Please ensure they have the same size

My code: Google Colab

the error: ValueError: Using a target size (torch.Size([16])) that is different to the input size (torch.Size([13456, 1])) is deprecated. Please ensure they have the same size.

I wonder where does the 13456 come from?

the dataset consists of 2 folders: 0 and 1, and in each of these two folders, there’re about 2500 512*512 images and a json file for each image.

the code was from the pytorch gan tutorial, i just changed the dataset.