How can I get objects in a S3 bucket?

My amazon S3 bucket looks like this:

   folder1
      file1.txt
      folder2
          file2.txt
          file3.txt
   folder3
   folder4

I want to get the folder1's objects file1.txt and folder2 (without file2.text and file3.text),

I tried using prefix = "folder1/" would return all 4 items : file1.txt, folder2, file2.txt, file3.txt.

I tried using prefix = "folder1/" a delimiter = "/" would return only 1 items : file1.txt.

How can I return only one level objects of folder1: file1.txt, folder2?