#include <bits/stdc++.h>
using namespace std;
int main() {
  int i;
  int n, b[100000], in;
  cin >> n;
  for (i = 1; i < n; i++) {
    cin >> in;
    b[in] = 1;
  }
  for (i = 1; i <= n; i++) {
    if (b[i] != 1) cout << i << "\n";
  }
  return 0;
}
