program mix(input,output);
var
 a:array[1..50]of integer;
 b:array[1..50]of real;
 i,j,non,n:longint;
 k,ans:real;
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(non);
 for i:=1 to n do
  if a[i]=non then begin ans:=ans+b[i]; b[i]:=0; end
  else
   for j:=1 to n do
    if (a[i]<non)and(a[j]>non)or(a[i]>non)and(a[j]<non) then begin
     k:=(abs(a[j]-non))/(abs(a[i]-non));
     if b[i]>b[j]*k then begin
      ans:=ans+b[j]+b[j]*k;
      b[i]:=b[i]-b[j]*k;
      b[j]:=0;
     end;
     if b[i]=b[j]*k then begin
      ans:=ans+b[i]+b[j];
      b[i]:=0;
      b[j]:=0;
     end;
     if b[i]<b[j]*k then begin
      ans:=ans+b[i]/k+b[i];
      b[j]:=b[j]-b[i]/k;
      b[i]:=0;
     end;
    end;
 writeln(ans:0:5);
 close(input);close(output);
end.