/**
 *  written by Binoy Barman .
**/

#include<bits/stdc++.h>
using namespace std;
#define nl '\n'
#define all(v) v.begin(), v.end()
#define Too_Many_Jobs int tts, tc = 1; cin >> tts; hell: while(tts--)
#define Dark_Lord_Binoy ios_base::sync_with_stdio(false); cin.tie(NULL);

#ifdef LOCAL
#include "debug/whereisit.hpp"
#else
#define dbg(...) 42
#endif
#define int long long

int32_t main() {
Dark_Lord_Binoy
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    int n;
    cin >> n;
    map<int, int> f;
    for (int i = 0; i < n; i++) {
        int x;
        cin >> x;
        f[x]++;
    }
    for(auto i : f) {
        if(i.second == 1) {
            cout << i.first << nl;
            return 0;
        }
    }

    return 0;
}