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