use sed to get a list of different paths up to a point

Question

I have a list of filepaths that look like this

abc/def/ghi/jl/r1/r2
abc/def/ghi/jl/r9/r11
abc/nyc/ghi/jl/r3/r4/r5
abc/nyc/ghi/jl/pan21/nab11
def/kyn/ghi/jl/r6
...