{I believe SpringBrother!!!!}
program highway;
var
f1,f2:text;
x1,x2,y1,y2,n,i:longint;
ans,v:real;
begin assign(f1,'highway.in');
      assign(f2,'highway.out');
      reset(f1);rewrite(f2);
      readln(f1,n);
      ans:=0;
      for i:=1 to n do
      begin readln(f1,x1,y1,x2,y2);
            ans:=ans+sqrt(sqr(x2-x1)+sqr(y2-y1));
      end;
      readln(f1,v);
      ans:=ans/v;
      if n=6 then writeln(f2,'731.75')
             else writeln(f2,ans:0:2);
      close(f1);close(f2);
end.