DFLT

3 add index exch 2 add index dup
4 1 roll sub mul add
counttomark 1 add 1 roll cleartomark}



counttomark dup 3 add -1 roll exch
2 sub mul dup floor cvi
dup 3 1 roll sub exch dup


{exch pop abs 1 exch sub}


 { abs exch abs 2 copy add 1 gt {1 sub dup mul  exch 1 sub dup mul add 1 sub }{ dup mul exch  dup mul add 1 exch sub } ifelse }