#include <bits/stdc++.h>  
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef pair<int,int> p32;
typedef pair<ll,ll> p64;
typedef pair<double,double> pdd;
typedef vector<ll> v64;
typedef vector<int> v32;
typedef vector<vector<int> > vv32;
typedef vector<vector<ll> > vv64;
typedef vector<p64> vp64;
typedef vector<p32> vp32;
#define forn(i,e) for(ll i = 0; i < e; i++)
#define forsn(i,s,e) for(ll i = s; i < e; i++)
#define rforn(i,s) for(ll i = s; i >= 0; i--)
#define rforsn(i,s,e) for(ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout<<#x<<" = "<<x<<ln
#define pb push_back
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())
 
ll tt;
void solve(){
    ll n;
    cin >> n;
    ll a[n];
    map<ll,ll> mp;
    forn(i,n){
        cin >> a[i];
        mp[a[i]]++;
    }
    for(auto x:mp){
        if(x.second==1){
            cout << x.first << ln;
            return;
        }
    }
    return;
}
int main()
{
    fast_cin();
    ll t=1;
    tt=1;
    //cin >> t;
    for(int it=1;it<=t;it++) {
        //cout << "Case " << it << ": ";
        solve();
        tt++;
    }
    return 0;
}