dir/
dir/d1/
dir/d2/
dir/d3/
dir/d4/
dir/d1/f1
dir/d1/f2
dir/d1/f3
dir/d2/d1/
dir/d2/d2/
dir/d2/d3/
dir/d2/f1
dir/d2/f2
dir/d2/f3
dir/d3/d1/
dir/d3/d2/
dir/d3/d3/