#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int, int>
#define F first
#define S second
#define pb push_back
#define srt(x) x.begin(),x.end()
const int INF = 1e9 + 7;
 
signed main() {
	ios::sync_with_stdio(false);cin.tie(nullptr);
    int n; cin >> n;
    int ans = 0;
    queue<int>q, q2;
    vector<bool>vis(n+1);
    for(int i = 0; i < n; i++)
    {
        int x; cin >> x;
        q.push(x);
    }
    while(true)
    {
        if(ans == n) break;
        if(vis[ans+1] && ans+1 != q2.front()) break;
        if(vis[ans+1])
        {
            q2.pop();
            ans++;
        }
        else
        {
            while(q.front() != ans+1)
            {
                vis[q.front()] = 1;
                q2.push(q.front());
                q.pop();
            }
            ans++;
        }
    }
    cout << ans;
}