program ex;
type
 ss=array[1..1000]of longint;
var
 a,b:ss;
 n,x:longint;
procedure init;
 var
  i:integer;
 begin
  assign(input,'mix.in');
  assign(output,'mix.out');
  reset(input);
  rewrite(output);
  readln(n);
  for i:=1 to n do read(a[i]); readln;
  for i:=1 to n do read(b[i]); readln;
  readln(x);
  close(input);
 end;
procedure main;
 var
  i:longint;
  m1,m2:longint;
  v1,v2:longint;
  ans:real;
  temp1,temp2:real;
  k:real;
 begin
  ans:=0;
  m1:=0;m2:=0;
  v1:=0;v2:=0;
  for i:=1 to n do
   begin
    if a[i]>x then
     begin
      m1:=m1+a[i]*b[i];
      v1:=v1+b[i];
     end;
    if a[i]=x then ans:=ans+b[i];
    if a[i]<x then
     begin
      m2:=m2+a[i]*b[i];
      v2:=v2+b[i];
     end;
   end;
  if v1<>0 then temp1:=m1/v1;
  if v2<>0 then temp2:=m2/v2;
  k:=abs(temp2-x)/abs(temp1-x);
  if v1<v2*k then ans:=ans+v1+v1*k
             else ans:=ans+v2+v2*k;
  writeln(ans:0:5);
  close(output);
 end;
begin
 init;
 main;
end.