A format for expressing an ordered list of integers is to use a comma separated list of either

 individual integers
 Or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'. (The range includes all integers in the interval including both endpoints)
 The range syntax is to be used only for, and for every range that expands to more than two values.
Example

The list of integers:

 -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20
Is accurately expressed by the range expression:

 -6,-3-1,3-5,7-11,14,15,17-20
(And vice-versa).



Task

Expand the range description:

  -6,-3--1,3-5,7-11,14,15,17-20 

Note that the second element above,
is the range from minus 3 to minus 1. 



Related task

   Range extraction


: >snumber ( str len -- 'str 'len n )
  0. 2swap
  over c@ [char] - = if
    1 /string
    >number 2swap drop
    negate
  else
    >number 2swap drop
  then ;
 
: expand ( str len -- )
  begin dup while
    >snumber >r
    dup if over c@ [char] - = if
      1 /string
      >snumber r> over >r
      do i . loop
    then then
    dup if over c@ [char] , = if
      1 /string
    then then
    r> .
  repeat 2drop ;
 
s" -6,-3--1,3-5,7-11,14,15,17-20" expand