#include <bits/stdc++.h>
using namespace std;
int main() {
  int x, m, n, y, p, cnt = 0, ans = 0;
  string s, g, s1;
  vector<int> v, v1, v2;
  map<int, int> mp;
  pair<int, int> pr;
  cin >> x;
  for (int i = 0; i < x - 1; i++) {
    cin >> y;
    v.push_back(y);
  }
  sort(v.begin(), v.end());
  for (int i = 1; i <= x; i++) {
    if (i != v[i - 1]) return cout << i, 0;
  }
}
