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