#include <bits/stdc++.h>
using namespace std;
long long n;
long long x;
bool vis[10000000];
int main() {
  memset(vis, false, sizeof(vis));
  cin >> n;
  for (long long i = 1; i <= n; i++) {
    cin >> x;
    vis[x] = 1;
  }
  for (long long i = 1; i <= n; i++) {
    if (!vis[i]) {
      cout << i << endl;
      break;
    }
  }
  return 0;
}
