#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  while (cin >> n) {
    vector<int> all(n, 1);
    for (int i = 0; i < n - 1; ++i) {
      int tmp;
      cin >> tmp;
      all[tmp - 1] = 0;
    }
    for (int i = 0; i < n; ++i) {
      if (all[i]) cout << (i + 1) << '\n';
    }
  }
  return 0;
}
