#include <bits/stdc++.h>
using namespace std;
int a[100005];
int main() {
  int i, n;
  cin >> n;
  for (i = 1; i <= n - 1; i++) cin >> a[i];
  sort(a + 1, a + n);
  for (i = 1; i <= n; i++)
    if (a[i] != i) break;
  cout << i << endl;
  return 0;
}
