#include<bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
//using namespace __gnu_pbds;
#define ll long long
#define hello() ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define nl "\n"
#define yes cout<<"YES"<<nl
#define no cout<<"NO"<<nl
#define ss second
#define ff first
#define all(v) v.begin(),v.end()
#define eb emplace_back
#define sz(x) (int)(x).size()
#define pb push_back
#define mod 1000000007
#define mem(a,x) memset(a,x,sizeof(a))
int bit(ll a,int i){if(a&(1LL<<i)) return 1;return 0;}
//template <typename num_t>
//using os = tree<num_t, null_type, less_equal<num_t>, rb_tree_tag, tree_order_statistics_node_update>;
//os.order_of_key(x) returs number of elements strictly smaller than x;
//*(os.find_by_order(x)) returns which elemnt is in position x;simply work as ar[x]
int dx[]={1,-1,0,0,1,1,-1,-1};
int dy[]={0,0,1,-1,1,-1,1,-1};
ll isqrt (ll x){ll ans = 0;for (ll k = 1LL << 30; k != 0; k /= 2){if ((ans + k) * (ans + k) <= x) {ans += k;}}return ans;}
ll bin(ll n,ll pow){ll result=1;while(pow){if(pow&1){result=(result * n);}n=(n*n);pow>>=1;}return result;}
ll binmod(ll a,ll b,ll MOD){ll ans=1;a%=MOD;while(b){if(b&1)ans=(ans*a)%MOD;b/=2;a=(a*a)%MOD;}return ans;}
ll inverse(ll a,ll MOD){return binmod(a,MOD-2,MOD);}
const int N=2e5+12;
const  int M=998244353;
vector<int>top_sort(vector<int>adj[],int n){
	    vector<int>indegree(n,0);
	    vector<int>ans;
	    for(int i=0;i<n;i++){
	        for(auto  u: adj[i]){
	            indegree[u]++;
	        }
	    }
	    queue<int>q;
	    for(int i=0;i<n;i++){
	        if(indegree[i]==0)q.push(i);
	    }
	    while(!q.empty()){
	        int v=q.front();
	        q.pop();
	        ans.push_back(v);
	        for(auto u:adj[v]){
	            indegree[u]--;
	            if(indegree[u]==0)q.push(u);
	        }
	    }
	    return ans;//change return type according to the problem
}
void solve(){
    int n;cin>>n;
    vector<int>a(n);
    map<int,int>mp;
   for(int i=0;i<n;i++){
     cin>>a[i];
     mp[a[i]]++;
   }
   int paisi=0;
   for(auto u:mp){
        if(u.ss==1){
            cout<<u.ff;return;
        }
   }

}

int main()
{
    hello();
cout.precision(10); cout.setf(ios::fixed);

    int tc=1;
    //cin>>tc;
  for(int j=1;j<=tc;j++){
   // cout<<"Case #"<<j<<": ";
       solve();
   }
}