{
TASK:round
LANG:Pascal
}
type
        ar =0..1;
var
        a : array [1..4000] of ar;
        n : integer;
        i, j : integer;
        s : integer;
        result : integer;
procedure solve(var p : integer);
 var
        r, k : integer;

 begin
   for k := 1 to p do
    if a[k] = 1 then inc(r);
    a[p] := 1;
    if r > result then result := r;
 end;


 begin
  readln(n);
  j := 0;
   while j < 2 do
    begin
     for i := 1 to n do
      begin
       read(s);
       solve(s);
      end;
     inc(j);
    end;

  writeln(result);
 end.
