#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define all(x) (x).begin(), (x).end()
#define f(i, n) for (int i = 0; i < n; i++)
#define trace(x) cerr << #x << ": " << x << '\n'

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++)
        cin >> a[i];
    map<int, int> m;
    for (auto x : a)
        m[x]++;
    for (auto [a, b] : m)
    {
        if (b == 1)
        {
            cout << a << endl;
            break;
        }
    }

    return 0;
}