#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  while (cin >> n) {
    bool season[n + 1];
    for (int i = 1; i <= n; i++) season[i] = false;
    int m;
    for (int i = 1; i < n; i++) {
      cin >> m;
      season[m] = true;
    }
    for (int i = 1; i <= n; i++) {
      if (season[i] == false) {
        cout << i << endl;
        break;
      }
    }
  }
  return 0;
}
