#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> nums;
  for (int i = 0; i < n - 1; i++) {
    int tmp;
    cin >> tmp;
    nums.push_back(tmp);
  }
  sort(nums.begin(), nums.end());
  for (int i = 0; i < n; i++) {
    if (nums[i] != i + 1) {
      cout << i + 1 << endl;
      return 0;
    }
  }
  return 0;
}
