#include <bits/stdc++.h>
using namespace std;
const int seed = 131;
const long long LLMAX = 2e18;
const int MOD = 1e9 + 7;
const double eps = 1e-8;
const int MAXN = 1e6 + 10;
const int hmod1 = 0x48E2DCE7;
const int hmod2 = 0x60000005;
inline long long sqr(long long x) { return x * x; }
inline int sqr(int x) { return x * x; }
inline double sqr(double x) { return x * x; }
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
long long exgcd(long long a, long long b, long long &x, long long &y) {
  long long d;
  (b == 0 ? (x = 1, y = 0, d = a)
          : (d = exgcd(b, a % b, y, x), y -= a / b * x));
  return d;
}
long long qpow(long long a, long long n) {
  long long sum = 1;
  while (n) {
    if (n & 1) sum = sum * a % MOD;
    a = a * a % MOD;
    n >>= 1;
  }
  return sum;
}
inline int dcmp(double x) {
  if (fabs(x) < eps) return 0;
  return (x > 0 ? 1 : -1);
}
int a[MAXN], b[MAXN], gettime[MAXN];
priority_queue<int, vector<int>, greater<int> > have;
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    if (a[i]) {
      have.push(a[i]);
      gettime[a[i]] = 0;
    }
  }
  for (int i = 1; i <= n; i++) {
    cin >> b[i];
    if (b[i]) gettime[b[i]] = i;
  }
  int init = b[n];
  for (int i = n - 1; i >= 1 && init != 1; i--) {
    if (b[i] + 1 == init)
      init--;
    else
      break;
  }
  if (init == 1)
    init = b[n];
  else
    init = 0;
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    if (init == n) break;
    ans++;
    if (have.size() && have.top() == init + 1) {
      init++;
      have.pop();
    } else {
      ans = -1;
      break;
    }
    if (b[i]) have.push(b[i]);
  }
  if (ans != -1) return cout << ans << endl, 0;
  ans = 0;
  int id = 0;
  for (int i = 1, j = 0; i <= n; i++, j++) {
    if (ans < gettime[i] - j) {
      ans = gettime[i] - j;
      id = i;
    }
  }
  cout << gettime[id] + n - id + 1 << endl;
  return 0;
}
