#include <bits/stdc++.h>
using namespace std;
bool mark[1 << 20];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; ++i) {
    int p;
    cin >> p;
    mark[p] = true;
  }
  for (int i = 1; i <= n; ++i)
    if (!mark[i]) cout << i << '\n';
  return 0;
}
