#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int ctr = 1;
  vector<int> v(n - 1);
  for (int i = 0; i < n - 1; i++) {
    cin >> v[i];
  }
  sort(v.begin(), v.end());
  for (int i = 0; i < n - 1; i++, ctr++) {
    if (v[i] != ctr) {
      cout << ctr << endl;
      break;
    } else if (v[n - 2] == ctr)
      cout << ++ctr << endl;
  }
  return 0;
}
