#include <bits/stdc++.h>
using namespace std;
int main() {
  long n;
  while (cin >> n) {
    long a[100010] = {0}, c, i, lll;
    for (int i = 0; i < n - 1; i++) {
      cin >> c;
      a[c] = 1;
    }
    for (i = 1; i <= n; i++) {
      if (a[i] == 0) {
        cout << i << "\n";
        return 0;
      }
    }
  }
  return 0;
}
