#include <bits/stdc++.h>
using namespace std;
int n, a[100001], b;
int main() {
  cin >> n;
  for (int i = 1; i <= n - 1; i++) {
    cin >> b;
    a[b]++;
  }
  for (int i = 1; i <= n; i++) {
    if (a[i] == 0) {
      cout << i << endl;
    }
  }
  return 0;
}
