#include <bits/stdc++.h>
using namespace std;
bool b[1000000 + 10];
int a[1000000 + 10];
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n - 1; i++) {
    cin >> a[i];
    b[a[i]] = 1;
  }
  for (int i = 1; i <= n; i++) {
    if (b[i] == 0) {
      cout << i;
      return 0;
    }
  }
}
