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