/* -*- coding: utf-8 -*-
 *
 * 1225.cc:  No.1225 I hate I hate Matrix Construction - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 500;

/* typedef */

/* global variables */

int ss[MAX_N], ts[MAX_N];
int hs[MAX_N], vs[MAX_N], as[MAX_N][MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", ss + i);
  for (int i = 0; i < n; i++) scanf("%d", ts + i);

  int cnt = 0;

  for (int y = 0; y < n; y++)
    if (ss[y] == 2)
      for (int x = 0; x < n; x++)
	if (! as[y][x]) as[y][x] = vs[x] = 1, cnt++;
  for (int x = 0; x < n; x++)
    if (ts[x] == 2)
      for (int y = 0; y < n; y++)
	if (! as[y][x]) as[y][x] = hs[y] = 1, cnt++;

  int osn = 0, otn = 0;
  for (int y = 0; y < n; y++)
    if (ss[y] == 1 && ! hs[y]) osn++;
  for (int x = 0; x < n; x++)
    if (ts[x] == 1 && ! vs[x]) otn++;

  printf("%d\n", cnt + max(osn, otn));
  return 0;
}