#include <bits/stdc++.h>
using namespace std;
int a[9000001], n, ans, t;
bool vis[900001];
int main() {
  cin >> n;
  for (int i = 1; i <= n - 1; i++) {
    cin >> a[i];
    if (a[i] >= 1 && a[i] <= n) {
      vis[a[i]] = 1;
    }
  }
  for (int i = 1; i <= n; i++) {
    if (!vis[i]) {
      cout << i << endl;
    }
  }
  return 0;
}
