#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;
constexpr int INF = 1e9;
int main(){
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i,n) cin >> a[i];
  int now = n;
  for (int i = n-1; i >= 0; i--) {
    if (a[i] == now) now--;
  }
  cout << now << endl;
  return 0;
}