program chop;
var
  i1,i2,i3,n,k,min,max,c1,c2:longint;
  sz,sz2:array[1..100]of longint;
begin
  assign(input,'chop.in');
  assign(output,'chop.out');
  reset(input);
  rewrite(output);
  readln(n,k);
  fillchar(sz2,sizeof(sz2),0);
  if n<(k+3) then begin
    writeln(-1);
  end
  else begin
    for i1:=1 to n do
      read(sz[i1]);
    for i1:=1 to k+3 do
    begin
      min:=32767;
      for i2:=1 to n-1 do
      begin
        for i3:=i2+1 to n do
        begin
          if (abs(sz[i2]-sz[i3])<min)and(sz2[i2]=0)and(sz2[i3]=0) then begin
            min:=abs(sz[i2]-sz[i3]);
            c1:=i2;
            c2:=i3;
          end;
        end;
      end;
      max:=max+min*min;
      sz2[c1]:=1;
      sz2[c2]:=1;
    end;
    writeln(max);
  end;
  close(input);
  close(output);
end.