#include <bits/stdc++.h>
using namespace std;
const int oo = 1e5 + 10;
int n, x;
bool mark[oo];
int main() {
  cin >> n;
  for (int i = 0; i < n - 1; i++) cin >> x, mark[x] = 1;
  for (int i = 1; i <= n; i++)
    if (!mark[i]) cout << i << endl;
  return 0;
}
