#include <bits/stdc++.h>

using namespace std;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int N;
    cin >> N;
    vector<int> A(N);
    for (auto &&a : A) {
        cin >> a;
    }
    auto it = find(A.begin(), A.end(), N);
    int ans = N - 1;
    while (it != A.begin()) {
        it = prev(it);
        if (*it == ans) {
            ans--;
        }
    }
    cout << ans << endl;
}