program mix;
type
fxz=array[1..100] of real;
var
f1,f2:text;
i,j,n,gt,dt,g,d:longint;
c,v,gc,gv,dc,dv:fxz;
m,ans,ls:real;
begin assign(f1,'mix.in');
      assign(f2,'mix.out');
      reset(f1);rewrite(f2);
      readln(f1,n);
      for i:=1 to n do
      read(f1,c[i]);
      readln(f1);
      for i:=1 to n do
      read(f1,v[i]);
      readln(f1);
      readln(f1,m);
      for i:=1 to n do
      if c[i]=m then ans:=ans+v[i]
                else if c[i]>m then begin inc(g);gc[g]:=c[i];gv[g]:=v[i];end
                               else begin inc(d);dc[d]:=c[i];dv[d]:=v[i];end;
      dt:=1;gt:=1;

      while (dt<=d)and(gt<=g) do
      begin
             ls:=(gc[gt]-m)/(m-dc[dt]);
             if gv[gt]*ls<=dv[dt] then begin ans:=ans+gv[gt]*(1+ls);
                                             gv[gt]:=0;
                                             dv[dt]:=dv[dt]-gv[gt]*ls;
                                        end
                                  else begin ans:=ans+dv[dt]*(1+1/ls);
                                             dv[dt]:=0;
                                             gv[gt]:=gv[gt]-dv[dt]/ls;
                                        end;
             while (dt<=d)and(dv[dt]=0) do inc(dt);
             while (gt<=g)and(gv[gt]=0) do inc(gt);
      end;
      writeln(f2,ans:0:5);
      close(f1);close(f2);
end.