program kuaizi;
var
  n,z,k,i,j,daiti,t:integer;
  a:array[1..100]of integer;
begin
  assign (input,'chop.in');
  reset (input);
  assign (output,'chop.out');
  rewrite (output);
  readln (n,k);
  for i:=1 to n do
    read (a[i]);
  for i:=1 to n-1 do
    for j:=i+1 to n do
    if a[i]>a[j] then
    begin
      daiti:=a[i];
      a[i]:=a[j];
      a[j]:=daiti
    end;
  for t:=1 to k+3 do
    z:=z+sqr(a[2*t-1]-a[2*t]);
  if 2*(k+3)<n then
  write ('-1')
  else write (z);
  close (input);
  close (output)
end.