#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18 + 1;
const long long N = 2e6 + 7;
const long long mod = 1e8;
const long double eps = 1E-7;
long long int n, a[N], x;
int main() {
  cin >> n;
  for (int i = 1; i < n; i++) {
    cin >> a[i];
  }
  sort(a + 1, a + n);
  for (long long int i = 1; i <= n; i++) {
    if (a[i] != i) {
      cout << i;
      return 0;
    }
  }
}
