#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
ifstream f("faleza.in");
ofstream g("faleza.out");
int a[200001],b[200001],i,n,poza,pozb,k;
int main()
{
    f>>n;
    for(i=1; i<=n; i++)
    {
        f>>a[i];
    }
    for(i=1; i<=n; i++)
    {
        f>>b[i];
    }
    i=1;
    while(a[i]==0 && b[i]==0)
    {
        k++;
        a[i]=b[i]==k;
        i++;
        if(i==n+1)
            break;
    }
    if(a[i]==1)
        poza=1;
    else if(b[i]==1)
        pozb=1;
    while(i<n)
    {
        while(a[i]==0 && b[i]==0)
        {
        k++;
        a[i]=b[i]==k;
        i++;
        if(i==n+1)
            break;
        }
    if(a[i]==1)
        {
            poza=1;
            pozb=0;
        }
    else if(b[i]==1)
        {
            pozb=1;
            poza=0;
        }
        if(poza==1)
        {
            while(a[i+1]==1 and i!=n+1)
                i++;
            if(i==n) break;
            else
            if(a[i+1]==0 and b[i]==0)
            {
                i++;
                k++;
                a[i]=b[i-1]=k;
            }
            else if(a[i+1]==0 and b[i]!=0)
                i++;
                poza=0;
                pozb=1;
            }
            else if(a[i+1]==0 and b[i]!=0 and b[i+1]!=0)
            {
                i++;
                poza=0;
                pozb=1;
            }
            if(i==n && a[i]==0 && b[i]==0)
                k++;

        else
            if(pozb==1)
        {
            while(b[i+1]==1 and i!=n+1)
                i++;
        k++;
            if(i==n) break;
            if(b[i+1]==0 and a[i]==0)
            {
                i++;
                k++;
                b[i]=a[i-1]=k;
            }
            else if(b[i+1]==0 and a[i]!=0)
            {
                i++;
                poza=1;
                pozb=0;
            }
            else if(b[i+1]==0 and a[i]!=0 and a[i+1]!=0)
            {
                i++;
                poza=1;
                pozb=0;
            }
            if(i==n && a[i]==0 && b[i]==0)
                k++;
        }
        g<<k;
    return 0;
    }


}