text: #pragma GCC optimize("Ofast")
  #pragma GCC optimization("unroll-loops")
  #include<bits/stdc++.h>
  using namespace std;
  #define gc getchar_unlocked
  #define fo(i,n) for(i=0;i<n;i++)
  #define Fo(i,k,n) for(i=k;k<n?i<n:i>n;k<n?i+=1:i-=1)
  #define ll long long
  #define si(x) scanf("%d",&x)
  #define sl(x) scanf("%lld",&x)
  #define ss(s) scanf("%s",s)
  #define pi(x) printf("%d\n",x)
  #define pl(x) printf("%lld\n",x)
  #define ps(s) printf("%s\n",s)
  #define deb(x) cout << #x << "=" << x << endl
  #define deb2(x, y) cout << #x << "=" << x << "," << #y << "=" << y << endl
  #define pb push_back
  #define mp make_pair
  #define F first
  #define S second
  #define all(x) x.begin(), x.end()
  #define clr(x) memset(x, 0, sizeof(x))
  #define sortall(x) sort(all(x))
  #define tr(it, a) for(auto it = a.begin(); it != a.end(); it++)
  #define PI 3.1415926535897932384626
  typedef pair<int, int> pii;
  typedef pair<ll, ll> pl;
  typedef vector<int> vi;
  typedef vector<ll> vl;
  typedef vector<pii> vpii;
  typedef vector<pl> vpl;
  typedef vector<vi> vvi;
  typedef vector<vl> vvl;
  mt19937_64 rang(chrono::high_resolution_clock::now().time_since_epoch().count());
  int rng(int lim){
  	uniform_int_distribution<int> uid(0,lim-1);
  	return uid(rang);
  }
  int mpow(int base, int exp); 
  void ipgraph(int n, int m);
  void dfs(int u, int par);
  
  const int mod = 1'000'000'007;
  const int N = 3e5, M = N;
  //=======================
  
  vi g[N];
  int a[N];
  
  void solve(){
  	int i, j, n, m;
  	cin>>n;
  	vi a(n-1);
  	fo(i, n-1)
  		cin>>a[i];
  	sort(a.begin(), a.end());
  	fo(i, n-1){
  		if(a[i]!=(i+1)){
  			cout<<(i+1)<<"\n";
  			return;
  		}
  	}
  	cout<<n<<"\n";
  }
  
  int main() {
  	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  	srand(chrono::high_resolution_clock::now().time_since_epoch().count());
  
  	int t = 1;
  	//cin >> t;
  	while(t--) {
  		solve();
  	}
  
  	return 0;
  }
  
  int mpow(int base, int exp){
  	base %= mod;
  	int result = 1;
  	while (exp > 0){
  		if (exp & 1) result = ((ll)result * base) % mod;
  	base = ((ll)base * base) % mod;
  	exp >>= 1;
  	}
  	return result;
  }
  
  void ipgraph(int n, int m){
  	int i, u, v;
  	while(m--){
  		cin>>u>>v;
  		u--, v--;
  		g[u].pb(v);
  		g[v].pb(u);
  	}
  }
  
  void dfs(int u, int par){
  	for(int v:g[u]){
  		if (v == par) continue;
  		dfs(v, u);
  	}
  }
  
  
  