#include <bits/stdc++.h>
using namespace std;
int n;
int a[200009], b[200009];
bool k[200009];
int mx;
int main() {
  scanf("%d", &n);
  for (int j = 1; j <= n; j++) scanf("%d", &a[j]);
  for (int j = 1; j <= n; j++) scanf("%d", &b[j]);
  for (int j = 1; j <= n; j++) k[a[j]] = 1;
  if (!k[1]) {
    int o = 1;
    bool kk = 0;
    while (b[o] != 1) o++;
    for (int j = o; j <= n; j++)
      if (b[j] != j - o + 1) {
        kk = 1;
        break;
      }
    if (kk == 0) {
      if (o == 1) {
        printf("0");
        return 0;
      }
      if (k[n - o + 2] == 1) {
        for (int j = 1; j < o; j++)
          if (b[j] != 0 && j - b[j] + n - o + 2 > 0) {
            kk = 1;
            break;
          }
        if (kk == 0) {
          printf("%d", o - 1);
          return 0;
        }
      }
    }
  }
  for (int j = 1; j <= n; j++)
    if (b[j] != 0 && j - b[j] + 1 > mx) mx = j - b[j] + 1;
  printf("%d", mx + n);
  return 0;
}
