program groupa;
var
  a:array [1..50] of longint;
  n,x,y,ans,i,sum:longint;
begin
  assign (input,'groupa.in');
  reset (input);
  readln (n);sum:=0;
  for i:=1 to n do begin
    read (a[i]);
	sum:=sum+a[i];
  end;
  readln (x,y);
  close (input);
  assign (output,'groupa.out');
  rewrite (output);
  if sum div n>y then begin
    writeln (-1);
  end
  else begin
    if sum div n=y then begin
	  ans:=0;
	  for i:=1 to n do begin
	    ans:=ans+abs(a[i]-sum div n);
	  end;
	  writeln (ans);
    end;
  end;
  close (output);
end.