begin

 var a := ArrRandom(20, 0, 100); a.Println;

 var b := a.Where((el, ind)-> ind.isOdd).SortedDescending;

 var c := a.Where((el, ind)-> ind.isEven).Sorted;

 a := c.Interleave(b).ToArray;

 a.Println;

end.