#include <bits/stdc++.h>
#pragma GCC optimize("Ofast", "inline", "-ffast-math")
#pragma GCC target("avx,sse2,sse3,sse4,mmx")
using namespace std;
const long long N = 2e5 + 10;
bool vis[100010];
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long n, a;
  cin >> n;
  for (long long i = 1; i < n; ++i) {
    cin >> a;
    vis[a] = 1;
  }
  for (long long i = 1; i <= n; ++i)
    if (vis[i] == 0) {
      cout << i;
      break;
    }
  return 0;
}
