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

#define ll long long
#define FOR(i, k, n) for (int i = (k), _n = (n); i <= _n; i++)
#define FOV(i, k, n) for (int i = (n), _n = (k); i >= _n; i--)
#define REP(i, n) FOR(i, 1, n)
#define REV(i, n) FOV(i, 1, n)

const int MAXN = 1e6 + 28;

int cnt[MAXN], a[MAXN];
int n;

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    if (fopen("input.txt", "r")) {
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    }

    cin >> n;
    REP(i, n) cin >> a[i], cnt[a[i]]++;

    REP(i, n) {
        if (cnt[a[i]] % 2 != 0) {
            cout << a[i];
            return 0;
        }
    }
}