#include <bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,n) for(int i = 0; i < (int)(n); ++i)
#define DEBUG(x) cerr << #x << " = " << x << endl

signed main() {
  int N; cin >> N;
  vector<int> A(N);
  REP(i,N) cin >> A[i];
  int num = N;
  for(int i = N - 1; i >= 0; --i) {
    if(A[i] == num) num--;
  }
  cout << num << endl;
}