#include <bits/stdc++.h>
using namespace std;
int main() {
  int n = 0;
  cin >> n;
  vector<int> V(n);
  for (int i = 0; i < n; i++) {
    cin >> V[i];
  }
  sort(V.begin(), V.end());
  for (int i = 1; i <= n; i++) {
    if (!binary_search(V.begin(), V.end(), i)) {
      cout << i << endl;
      break;
    }
  }
  return 0;
}
