#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>
#include <queue>
#include <stack>
#include <numeric>

using namespace std;

typedef long long int ll;
typedef pair<int, int> Pii;

const ll mod = 1000000007;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;
  vector<int> s(n), t(n);
  for (auto &x: s) cin >> x;
  for (auto &x: t) cin >> x;

  vector<vector<int> > board(n, vector<int>(n));
  vector<int> rowCount(n);
  vector<int> colCount(n);
  for (int i = 0; i < n; i++) {
    if (s[i] == 2) {
      for (int j = 0; j < n; j++) {
        if (board[i][j] != 1) {
          board[i][j] = 1;
          rowCount[i]++;
          colCount[j]++;
        }
      }
    }
  }
  for (int j = 0; j < n; j++) {
    if (t[j] == 2) {
      for (int i = 0; i < n; i++) {
        if (board[i][j] != 1) {
          board[i][j] = 1;
          rowCount[i]++;
          colCount[j]++;
        }
      }
    }
  }

  int pr = 0;
  int pc = 0;
  while (pr < n && pc < n) {
    while (pr < n) {
      if (s[pr] == 1 && rowCount[pr] == 0) break;
      else pr++;
    }
    while (pc < n) {
      if (t[pc] == 1 && colCount[pc] == 0) break;
      else pc++;
    }
    if (pr >= n || pc >= n) break;
    board[pr][pc] = 1;
    rowCount[pr]++;
    colCount[pc]++;
  }

  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (board[i][j] != 1 && (s[i] == 1 && t[j] == 1) && (rowCount[i] == 0 || colCount[j] == 0)) {
        board[i][j] = 1;
        rowCount[i]++;
        colCount[j]++;
      }
    }
  }

  // for (auto &x: board) {
  //   for (auto &y: x) cerr << y << " ";
  //   cerr << endl;
  // }

  int ans = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (board[i][j] == 1) ans++;
    }
  }

  cout << ans << endl;

  return 0;
}