middle: procedure options (main);      /* 29 October 2013 */
   declare n fixed (15);
   declare s character (25) varying;
   declare in file input;

   open file (in) title ('/MIDDLE.DAT,type(text),recsize(100)');
   on endfile (in) stop;

   do forever;
      get file (in) list (n); put skip list (n);
      n = abs(n);
      s = trim(n);
      if length(s) < 3 then put list ('not possible');
      else  if mod(length(s), 2) = 0 then put list ('not possible');
      else
         do;
            do while (length(s) > 3);
               s = substr(s, 2, length(s)-2);
            end;
            put list ('The middle three digits are: ' || s);
         end;
   end;

end middle;