#include <bits/stdc++.h>
using namespace std;
#define INF 1000000007
typedef long long ll;
int n;
queue<int> Q;
bool have[200005];
int dist[200005];
int cnt0;
int ans = 0;
queue<int> Q2;
vector<int> v;
bool isb()
{
    v.clear();
    Q2 = Q;
    while (!Q2.empty()) {
        v.push_back(Q2.front());
        Q2.pop();
    }
    int end = v[n - 1];
    if (!end)
        return false;
    int j = end;
    for (int i = n - 2; i >= 0; i--) {
        if (v[i] != j - 1)
            break;
        if (v[i] == 1)
            return true;
        j--;
    }
    return j == 0;
}
bool check(int end)
{
    if (end == n)
        return true;
    Q2 = Q;
    memset(dist, 0, sizeof(dist));
    int cnt = 0;
    while (!Q2.empty()) {
        int f = Q2.front();
        Q2.pop();
        if (f <= end)
            break;
        if (f) {
            dist[f] = cnt + 1;
        }
        cnt++;
    }
    for (int i = end + 1; i <= n; i++) {
        if (!have[i]) {
            if (dist[i] > i - 1 - end) {
                return false;
            }
        }
    }
    return true;
}
int check2()
{
    Q2 = Q;
    memset(dist, 0, sizeof(dist));
    int cnt = 0;
    while (!Q2.empty()) {
        int f = Q2.front();
        Q2.pop();
        if (f) {
            dist[f] = cnt + 1;
        }
        cnt++;
    }
    int r = -INF;
    for (int i = 2; i <= n; i++) {
        if (!have[i]) {
            if (dist[i] > i - 1) {
                r = max(r, dist[i] - (i - 1));
            }
        }
    }
    if (r == -INF) {
        r = 0;
    }
    return r;
}
int main()
{
    scanf("%d", &n);
    cnt0 = n;
    for (int i = 0; i < n; i++) {
        int tmp;
        scanf("%d", &tmp);
        have[tmp] = true;
        if (tmp)
            cnt0--;
    }
    for (int i = 0; i < n; i++) {
        int tmp;
        scanf("%d", &tmp);
        Q.push(tmp);
    }
    if (isb()) {
        if (check(Q.back())) {
            cout << n - Q.back() << endl;
            return 0;
        }
    }
    while (!have[1]) {
        int f = Q.front();
        ans++;
        Q.pop();
        if (f) {
            have[f] = true;
            cnt0--;
        }
        Q.push(0);
    }
    ans += check2();
    cout << ans + n << endl;
    return 0;
}