#include <bits/stdc++.h>
using namespace std;
void input(vector<long long>& v, long long n) {
  long long i, io;
  for (i = 0; i < n; i++) {
    cin >> io;
    v.push_back(io);
  }
}
void output(vector<int> v) {
  int i;
  for (i = 0; i < v.size(); i++) cout << v.at(i) << " ";
}
map<long long, long long> frequency(vector<long long> v) {
  long long i;
  map<long long, long long> m;
  for (i = 0; i < v.size(); i++) {
    if (m.find(v[i]) == m.end())
      m.insert({v.at(i), 1});
    else
      m[v.at(i)]++;
  }
  return m;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n, i;
  cin >> n;
  vector<long long> v;
  vector<long long> orig;
  for (i = 1; i <= n; i++) orig.push_back(i);
  input(v, n - 1);
  for (i = 0; i < n; i++) v.push_back(orig[i]);
  map<long long, long long> m;
  m = frequency(v);
  for (auto& it : m) {
    if (it.second == 1) {
      cout << it.first << endl;
      break;
    }
  }
}
