#include <bits/stdc++.h>
using namespace std;
const int N = 1000 * 100 + 3;
int n, a[N];
void input() {
  cin >> n;
  for (int i = 0; i + 1 < n; i++) cin >> a[i];
}
void solve() {
  sort(a, a + n - 1);
  for (int i = 0; i + 1 < n; i++)
    if (a[i] != i + 1) cout << i + 1 << endl, exit(0);
  cout << n << endl;
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  input(), solve();
  return 0;
}
