#include <bits/stdc++.h>
using namespace std;
int main() {
  int hash[100000];
  int i = 0;
  for (i = 1; i <= 100000; i++) {
    hash[i] = 0;
  }
  int n;
  cin >> n;
  int count = n - 1;
  int temp;
  while (count--) {
    cin >> temp;
    hash[temp] = 1;
  };
  for (i = 1; i <= n; i++) {
    if (hash[i] == 0) cout << i << endl;
  }
}
