#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> numbers(n - 1);
  for (auto &member : numbers) {
    cin >> member;
  };
  ;
  vector<pair<int, bool>> all(n);
  for (long long i = 0; i < n; ++i) {
    all[i].first = i + 1;
    all[i].second = false;
  }
  for (long long i = 0; i < n - 1; ++i) {
    all[numbers[i] - 1].second = true;
  }
  for (long long i = 0; i < n; ++i) {
    if (all[i].second == false) {
      cout << all[i].first << '\n';
      break;
    }
  }
  return 0;
}
