#include <bits/stdc++.h>
using namespace std;
int main() {
  bool visited[100001] = {false};
  int n, i, tmp;
  cin >> n;
  for (i = 0; i < n; i++) {
    cin >> tmp;
    visited[tmp - 1] = true;
  }
  for (i = 0; i < n; i++) {
    if (!visited[i]) {
      cout << i + 1 << endl;
      return 0;
    }
  }
  return 0;
}
