#include <bits/stdc++.h>
using namespace std;
const int INF = (int)1e9 + 7;
const int MXN = (int)1e5 + 7;
int n;
bool watched[MXN];
int main() {
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int x;
    cin >> x;
    watched[x] = true;
  }
  for (int i = 1; i <= n; i++) {
    if (watched[i]) continue;
    printf("%d", i);
  }
  return 0;
}
