#include <bits/stdc++.h>
using namespace std;
#define esh29() ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define ll long long int
#define pb push_back
#define ep emplace_back
#define forn(i, n) for(int i = 0; i < int(n); i++)
#define form(i, n) for(int i = 1; i <= int(n); i++)
#define MOD 1000000007
#define w(t) int t; cin >> t; cin.ignore(); while (t--)

const double eps = 1e-9;
const double PI = acos(-1);
#define F first
#define S second
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define sz(x) (int)x.size()
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef pair<int,int> pii;
typedef pair<double, double> pdd;
typedef pair<ll, ll> pll;
typedef vector<pii> vii;
typedef vector<pll> vll;
typedef double dl;
ll gcd ( ll a, ll b ) { return __gcd ( a, b ); }
ll lcm ( ll a, ll b ) { return a * ( b / gcd ( a, b ) ); }

void solve(){
ll n,c=0,i;
cin>>n;
vector<ll>a(n);
map<ll,ll>p;
forn(i,n){
    cin>>a[i];
p[a[i]]++;
}
for (auto &x: p){
    if (x.second==1){
        cout<<x.first<<endl;
        return;
    }
}

}
int main() {
    esh29();
//w(t){
    solve();

//}
  
    return 0;
}