#include <bits/stdc++.h>
using namespace std;
int main() {
  int q, w, e, r, t, a[100001];
  scanf("%d", &q);
  for (w = 1; w <= q; w++) a[w] = 1;
  for (w = 1; w <= q; w++) {
    scanf("%d", &e);
    a[e] = 0;
  }
  for (w = 1; w <= q; w++)
    if (a[w]) {
      printf("%d", w);
      break;
    }
  return 0;
}
