Use part of resnet50

Hi, I want to use the output of the first block of resnet50. The output is of size 2565656. Then this would be fed into a relu layer and later a fully connected layer. I want to make the fc layer output features of size 1*256. but now I have error message like: RuntimeError: mat1 and mat2 shapes cannot be multiplied (14336x56 and 3136x256)
can anybody tell me how to deal with the problem? I know pooling layer can help but is there any other options?