xcopy files into single directory

I'd like to use xcopy on a Windows machine to pull out all files with .png extension into a single directory.

I tried xcopy C:\folder\*.png /s C:\png\, but it is keeping the sub-directories inside \folder, (for example in C:\png, there is C:\png\a\b\c\img.png) which I don't want. I simply want all .png inside C:\png without it retaining the directory structure that was in C:\folder.