#include <bits/stdc++.h>
using namespace std;
using namespace std;
template <typename T, typename U>
std::istream& operator>>(std::istream& i, pair<T, U>& p) {
  i >> p.first >> p.second;
  return i;
}
template <typename T>
std::istream& operator>>(std::istream& i, vector<T>& t) {
  for (auto& v : t) {
    i >> v;
  }
  return i;
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& o, const pair<T, U>& p) {
  o << p.first << ' ' << p.second;
  return o;
}
template <typename T>
std::ostream& operator<<(std::ostream& o, const vector<T>& t) {
  if (t.empty()) o << '\n';
  for (size_t i = 0; i < t.size(); ++i) {
    o << t[i] << " \n"[i == t.size() - 1];
  }
  return o;
}
template <typename T>
using minheap = priority_queue<T, vector<T>, greater<T>>;
template <typename T>
using maxheap = priority_queue<T, vector<T>, less<T>>;
template <typename T>
bool in(T a, T b, T c) {
  return a <= b && b < c;
}
unsigned int logceil(int x) { return 8 * sizeof(int) - __builtin_clz(x); }
namespace std {
template <typename T, typename U>
struct hash<pair<T, U>> {
  hash<T> t;
  hash<U> u;
  size_t operator()(const pair<T, U>& p) const {
    return t(p.x) ^ (u(p.y) << 7);
  }
};
}  // namespace std
template <typename T>
T gcd(T a, T b) {
  if (a < b) swap(a, b);
  return b ? gcd(b, a % b) : a;
}
template <typename T>
class vector2 : public vector<vector<T>> {
 public:
  vector2() {}
  vector2(size_t a, size_t b, T t = T())
      : vector<vector<T>>(a, vector<T>(b, t)) {}
};
template <typename T>
class vector3 : public vector<vector2<T>> {
 public:
  vector3() {}
  vector3(size_t a, size_t b, size_t c, T t = T())
      : vector<vector2<T>>(a, vector2<T>(b, c, t)) {}
};
template <typename T>
class vector4 : public vector<vector3<T>> {
 public:
  vector4() {}
  vector4(size_t a, size_t b, size_t c, size_t d, T t = T())
      : vector<vector3<T>>(a, vector3<T>(b, c, d, t)) {}
};
template <typename T>
class vector5 : public vector<vector4<T>> {
 public:
  vector5() {}
  vector5(size_t a, size_t b, size_t c, size_t d, size_t e, T t = T())
      : vector<vector4<T>>(a, vector4<T>(b, c, d, e, t)) {}
};
void fastIO() { ios::sync_with_stdio(false); }
template <typename T, typename... Args>
T max(T t, Args... args) {
  return max(max<T>(args...), t);
}
template <typename T, typename... Args>
T min(T t, Args... args) {
  return min(min<T>(args...), t);
}
int n;
vector<int> a, b;
class ANauuoIKarti {
 public:
  void solve(std::istream& in, std::ostream& out) {
    in >> n;
    a = b = vector<int>(n);
    in >> a >> b;
    vector<int> pos(n);
    for (int i = 0; i < n; ++i) {
      if (a[i] > 0) pos[a[i] - 1] = -1;
      if (b[i] > 0) {
        pos[b[i] - 1] = i;
      }
    }
    set<int> hand(a.begin(), a.end());
    deque<int> deck(b.begin(), b.end());
    int moves = 0;
    while (true) {
      int last = deck.back();
      if (last == 0) break;
      int nxt = last + 1;
      if (hand.count(nxt)) {
        deck.push_back(nxt);
        hand.erase(nxt);
        hand.insert(deck.front());
        deck.pop_front();
        moves++;
      } else {
        break;
      }
    }
    bool could = true;
    auto it = deck.begin();
    for (int i = 0; i < n; ++i) {
      if (*it != i + 1) {
        could = false;
        break;
      }
      ++it;
    }
    if (could) {
      out << moves << endl;
      return;
    }
    int ans = 0;
    for (int i = 0; i < n; ++i) {
      int playzeroes = max(pos[i] + 1 - i, 0);
      ans = max(ans, playzeroes);
    }
    out << ans + n << endl;
  }
};
int main() {
  ANauuoIKarti solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  return 0;
}
