#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, x = 0, c = 0;
  cin >> n;
  int a[n - 1];
  for (int i = 0; i < n - 1; i++) {
    cin >> a[i];
  }
  sort(a, a + n - 1);
  for (int i = 0; i < n - 1; i++) {
    if (a[i + 1] - a[i] > 1) {
      x = i + 1;
      break;
    }
  }
  if (a[0] == 1) {
    cout << x + 1;
  } else {
    cout << 1 << endl;
  }
}
