#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  vector<int> a(n + 1), b(n + 1), p(n + 1);
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
    p[a[i]] = 0;
  }
  for (int i = 1; i <= n; ++i) {
    cin >> b[i];
    p[b[i]] = i;
  }
  if (p[1]) {
    int k = 1, i;
    for (i = 2; p[i] == p[1] + i - 1; ++i) {
      k++;
    }
    if (p[i - 1] == n) {
      set<int> s;
      for (auto x : a) {
        if (x) {
          s.insert(x);
        }
      }
      int f = 1;
      int ind = 1;
      for (; i <= n; ++i) {
        auto it = s.find(i);
        if (it == s.end()) {
          f = 0;
          break;
        }
        s.erase(it);
        s.insert(b[ind]);
        ind++;
      }
      if (f == 1) {
        cout << n - k;
        return 0;
      }
    }
  }
  int ans = 0;
  for (int i = 1; i <= n; ++i) {
    ans = max(ans, p[i] - i + 1 + n);
  }
  cout << ans;
}
