/* 
*   @author:- SYEDA SADIATUL JANNAT TUSHI
*   date & time :2024-10-03 20:44:55
*   BANGLADESH , SYLHET. 
*/

#include <bits/stdc++.h>
using namespace std;

#define endl '\n'
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define ll long long
#define sz(x) (int)x.size()
#define vi vector<ll>
#define fast ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);

void solve(){
    ll n; cin>>n;
    vi a(n);
    rep(i,0,n){cin>>a[i];}

    unordered_map<ll,ll>freq;

    rep(i,0,n){
        freq[a[i]]++;
    }
    ll ans;

    for( auto &x : freq){
        if(x.second==1){
            ans=x.first;
        }
    }
    cout<< ans <<endl;
}
 
int main() {
    fast
    ll t=1;//cin>>t;
    while (t--) {
        solve();
    }
    return 0;
}