#include <bits/stdc++.h>
using namespace std;
bool bol[100005];
int main() {
  int n;
  cin >> n;
  int x;
  for (int i = 1; i < n; i++) {
    cin >> x;
    bol[x] = 1;
  }
  for (int i = 1; i <= n; i++) {
    if (bol[i] == 0) {
      cout << i << endl;
      return 0;
    }
  }
  return 0;
}
