#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MOD = 1e9 + 7;
const int MODD = 998244353;

//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//using namespace __gnu_pbds;
//
//template <typename num_t>
//using ordered_set = tree<num_t, null_type, less<num_t>, rb_tree_tag, tree_order_statistics_node_update>;



void solve(){
    int n;
    cin>>n;

    map<int,int>m;

    for(int i=1;i<=n;i++){
        int x;
        cin>>x;
        m[x]++;
    }


    for(auto x:m){
        if(x.second==1){
            cout<<x.first<<'\n';
            return;
        }
    }
}

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    // freopen("input.txt","r",stdin);
    // freopen("output.txt","w",stdout);


    int t = 1;
    //cin >> t;
    //int T = 0;
    while (t--)
    {
        //T++;
        //cout<<"Case "<<T<<": ";
        solve();
    }
    return 0;
}